Microsoft Programmer's Library 1.3

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Microsoft(R) Macro Assembler Reference for the MS-DOS(R) and OS/2 Operating Systems Microsoft Corporation Information in this document is subject to change without notice and does not represent a commitment on the part of Microsoft Corporation. The software described in this document is furnished under a license agreement or nondisclosure agreement. The software may be used or copied only in accordance with the terms of the agreement. The purchaser may make one copy for backup purposes. No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, for any purpose other than the purchaser's personal use without the written permission of Microsoft Corporation. (C) Copyright Microsoft Corporation, 1987, 1988. All rights reserved. Simultaneously published in the U.S. and Canada. Printed and bound in the United States of America. Timings and encodings in this manual are used with permission of Intel and come from the following publications: Intel Corporation. iAPX 86, 88, 186 and 188 User's Manual, Programmer's Reference. Santa Clara, Calif. 1986. Intel Corporation. iAPX 286 Programmer's Reference Manual including the iAPX 286 Numeric Supplement, Santa Clara, Calif. 1985. Intel Corporation. 80386 Programmer's Reference Manual. Santa Clara, Calif. 1986 Intel Corporation. 80387 80-bit CHMOS III Numeric Processor Extension. Santa Clara, Calif. 1987. Intel Corporation. i486 Microprocessor, Santa Clara, Calif. 1989. Document No. 410610002-500-R01-1287 10 9 8 7 6 5 4 3 2 1 Part No. 04696 Document Conventions KEY TERMS Bold type indicates text that must be typed exactly as shown. This includes assembly-language instructions, directives, symbols, and operators, as well as keywords in other languages. placeholders Italics indicate variable information supplied by the user. Examples This typeface indicates example programs, user input, and screen output. [optional items] Double brackets indicate that the enclosed item is optional. {choice1 | choice2} Braces and a vertical bar indicate a choice between two or more items. You must choose one of the items unless double square brackets surround the braces. Repeating elements... Three dots following an item indicate that more items having the same form may be typed. SHIFT+F1 Small capital letters indicate key names. Tools BIND The BIND utility converts an OS/2 program to run under both DOS and OS/2. Command-Line Syntax BIND infile [libraries] [options] Options ╓┌───────────────────────────────────┌───────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /HELP Option name: /HELP. Calls QuickHelp for help on BIND. /MAP [ mapfile] Option name: /M[AP]. Generates a map of the DOS part of the executable file. /NAMES functions/NAMES @filename Option name: /N[AMES]. Specifies functions supported under OS/2 only. Use with a list of functions separated by spaces or a file specification preceded by @. Option Action ──────────────────────────────────────────────────────────────────────────── preceded by @. /NOLOGO Option name: /NOLOGO. Suppresses the BIND copyright message. /O outfile Option name: /O[UTFILE]. Specifies the name for the bound application. /? Option name: /?. Displays a brief summary of BIND command-line syntax. Environment Variables ╓┌───────────┌───────────────────────────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── LIB Specifies search path for library files. LINK Specifies default command-line options for the linker. TMPf Specifies path for the VM.TMP file. Microsoft(R) CodeView(R) Debugger The Microsoft(R) CodeView(R) debugger runs the assembled or compiled program while simultaneously displaying the program source code, program variables, memory locations, processor registers, and other pertinent information. Command-Line Syntax CV [options] executablefile [arguments] CVP [options] executablefile [arguments] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /2 Permits the use of two monitors. /25 Starts in 25-line mode. /43 Starts in 43-line mode. /50 Starts in 50-line mode. /B Starts in black-and-white mode. /C commands Executes commands on start-up. /D[ buffersize] Enables disk overlays (CV only). /E Enables use of expanded memory (CV only). /F Exchanges screens by flipping between Option Action ──────────────────────────────────────────────────────────────────────────── /F Exchanges screens by flipping between video pages (CV only). /G Eliminates refresh snow on CGA monitors (CV only). /I[0 | 1] Turns nonmaskable-interrupt and 8259-interrupt trapping on (/I1) or off (/I0) (CV only). /K Disables installation of keyboard monitors for the program being debugged. /L dll Loads symbolic information for the specified dynamic-link library (CVP only). /M Disables CodeView use of the mouse (use this option when debugging an Option Action ──────────────────────────────────────────────────────────────────────────── this option when debugging an application that supports the mouse). /N[0 | 1] /N0 tells CodeView to trap nonmaskable interrupts; /N1 tells it not to trap (CV only). /O Enables debugging of multiple processes (CVP only). /R Enables 80386/486 debug registers (CV only). /S Exchanges screens by changing buffers (primarily for use with graphics programs) (CV only). /TSF Toggles TOOLS.INI entry to read/not read the CURRENT.STS file. Option Action ──────────────────────────────────────────────────────────────────────────── the CURRENT.STS file. /X Enables use of extended memory (CV only). Environment Variables variable Description ──────────────────────────────────────────────────────────────────────────── HELPFILES Specifies path of help files or list of help filenames. INIT Specifies path for TOOLS.INI and CURRENT.STS files. CVPACK The CVPACK utility reduces the size of an executable file that contains CodeView debugging information. Command-Line Syntax CVPACK [options] exefile Options Option Action ──────────────────────────────────────────────────────────────────────────── /HELP Calls QuickHelp for help on CVPACK. /P Packs the file to the smallest possible size. /? Displays a brief summary of CVPACK command-line syntax. EXEHDR The EXEHDR utility displays and modifies the contents of an executable-file header. Command-Line Syntax EXEHDR [options] filenames Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option action ──────────────────────────────────────────────────────────────────────────── /HEAP: number Option name: /HEA[P]. Sets the heap allocation field to number bytes for segmented executable files. /HELP Option name: /HEL[P]. Calls QuickHelp for help on EXEHDR. /MAX: number Option name: /MA[X]. Sets the maximum Option action ──────────────────────────────────────────────────────────────────────────── /MAX: number Option name: /MA[X]. Sets the maximum memory allocation to number paragraphs for DOS executable files. /MIN: number Option name: /MI[N]. Sets the minimum memory allocation to number paragraphs for DOS executable files. /NEW Option name: /NE[WFILES]. Enables support for HPFS. /NOLOGO Option name: /NO[LOGO]. Suppresses the EXEHDR copyright message. /PM: type Option name: /P[MTYPE]. Sets the application type for OS/2 or Microsoft Windows[tm], where type is one of the Option action ──────────────────────────────────────────────────────────────────────────── Windows[tm], where type is one of the following: PM (or WINDOWAPI), VIO (or WINDOWCOMPAT), or NOVIO (or NOTWINDOWCOMPAT). /RESET Option name: /R[ESETERROR]. Clears the error bit in the header of an OS/2 or Windows executable file. /STACK: number Option name: /S[TACK]. Sets the stack allocation to number bytes. /V Option name: /V[ERBOSE]. Provides more information about segmented executable files, including the default flags in the segment table, all run-time relocations, and additional fields from the header. Option action ──────────────────────────────────────────────────────────────────────────── /? Option name: /?. Displays a brief summary of EXEHDR command-line syntax. EXP The EXP utility deletes all files in the hidden DELETED subdirectory of the current or specified directory. EXP is used along with RM and UNDEL to manage backup files. Command-Line Syntax EXP [options] [directories] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /HELP Calls QuickHelp for help on EXP. /Q Suppresses display of deleted files. /R Recurses into subdirectories of the current or specified directory. /? Displays a brief summary of EXP command-line syntax. HELPMAKE The HELPMAKE utility creates help files and customizes the help files supplied with Microsoft language products. Command-Line Syntax HELPMAKE {/E[n] | /D[c] | /H | /?} [options] sourcefiles Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /A c Specifies c as an application-specific control character for the help database, marking a line that contains special information for internal use by the application. /C Indicates that the context strings are case sensitive so that at run time all searches for help topics will be case sensitive. Option Action ──────────────────────────────────────────────────────────────────────────── sensitive. /D Fully decodes the help database. /DS Splits the concatenated, compressed help database into its components, using their original names. No decompression occurs. /DU Decompresses the database and removes all screen formatting and cross-references. /E[ n] Creates ("encodes") a help database from a specified text file (or files). The optional n indicates the amount of compression to take place. The value of n can range from 0 to 15. Option Action ──────────────────────────────────────────────────────────────────────────── /H[ELP] Calls the QuickHelp utility. If HELPMAKE cannot find QuickHelp or the help file, it displays a brief summary of HELPMAKE command-line syntax. /K filename Specifies a file containing word-separator characters. This file must contain a single line of characters that separate words. ASCII characters from 0 to 32 (including the space) and character 127 are always separators. If the /K option is not specified, the following characters are also considered separators: /L Locks the generated file so that it cannot be decoded by HELPMAKE at a later Option Action ──────────────────────────────────────────────────────────────────────────── cannot be decoded by HELPMAKE at a later time. /NOLOGO Suppresses the HELPMAKE copyright message. /O outfile Specifies outfile as the name of the help database. The name outfile is optional with the /D option. /S n Specifies the type of input file, according to the following n values: /T During encoding, translates dot commands to application-specific commands. During decoding, translates application commands to dot commands. The /T option Option Action ──────────────────────────────────────────────────────────────────────────── commands to dot commands. The /T option forces /A:. /V[ n] Sets the verbosity of the diagnostic and informational output, depending on the value of n. The value of n can range from 0 to 6. /W width Sets the fixed width of the resulting help text in number of characters. The value of width can range from 11 to 255. /? Displays a brief summary of HELPMAKE command-line syntax. H2INC The H2INC utility converts C header (.H) files into MASM- compatible include (.INC) files. It translates declarations and prototypes, but does not translate code. Command-Line SyntaxH2INC [options] filename.H Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /C Passes comments in the .H file to the .INC file. /Fa [ filename] Specifies that the output file contain only equivalent MASM statements. This is the default. /Fc [ filename] Specifies that the output file contain Option Action ──────────────────────────────────────────────────────────────────────────── /Fc [ filename] Specifies that the output file contain equivalent MASM statements plus original C statements converted to comment lines. /HELP Calls QuickHelp for help on H2INC. /Ht Enables generation of text equates. By default, text items are not translated. /Mn Instructs H2INC to explicitly declare the distances for all pointers and functions. /Ni Suppresses the expansion of nested include files. /Zn string Adds string to all names generated by H2INC. Used to eliminate name conflicts with other H2INC-generated include files. Option Action ──────────────────────────────────────────────────────────────────────────── with other H2INC-generated include files. /Zu Makes all structure and union tag names unique. /? Displays a brief summary of H2INC command-line syntax. Note: H2INC also supports the following options from Microsoft C, version 6.0: /AC, /AH, /AL, /AM, /AS, /AT, /D, /F, /Fi, /G0, /G1, /G2, /G3, /G4, /Gc, /Gd, /Gr, /I, /J, /Tc, /U, /u, /W0, /W1, /W2, /W3, /W4, /X, /Za, /Zc, /Ze, /Zp1, /Zp2, /Zp4. Environment Variables ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── CL Specifies default command-line options. H2INC Specifies default command-line options. Appended after the CL environment variable. INCLUDE Specifies search path for include files. IMPLIB The IMPLIB utility creates import libraries used by LINK to link dynamic-link libraries with applications. Command-Line Syntax IMPLIB [options] implibname {dllfile... | deffile...} Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option action ──────────────────────────────────────────────────────────────────────────── /HELP Option name: /H[ELP]. Calls QuickHelp for help on IMPLIB. /NOI Option name: /NOI[GNORECASE]. Preserves case for entry names in DLLs. /NOLOGO Option name: /NOL[OGO]. Suppresses the IMPLIB copyright message. /? Option name: /?. Displays a brief summary of IMPLIB command-line syntax. LIB The LIB utility helps create, organize, and maintain run-time libraries. Command-Line SyntaxLIB inlibrary [options] [commands] [, [listfile] [, [outlibrary] ] ] [;] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /HELP /IGN Option name: /I[GNORECASE]. Tells LIB to ignore case when comparing symbols (the default). Use to combine a library marked /NOI with an unmarked library to create a new case-insensitive library. Option Action ──────────────────────────────────────────────────────────────────────────── create a new case-insensitive library. /NOE Option name: NOE[XTDICTIONARY]. Prevents LIB from creating an extended dictionary. /NOI Option name: /NOI[GNORECASE]. Tells LIB to preserve case when comparing symbols. When combining libraries, if any library is marked /NOI, the output library is case sensitive, unless /IGN is specified. /NOLOGO Option name: /NOL[OGO]. Suppresses the LIB copyright message. /PAGE: number Option name: /P[AGESIZE]. Specifies the page size (in bytes) of a new library or changes the page size of an existing library. The default for a new library is 16. Option Action ──────────────────────────────────────────────────────────────────────────── is 16. /? Option name: /?. Displays a brief summary of LIB command-line syntax. Commands ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Operator Action ──────────────────────────────────────────────────────────────────────────── + name Appends an object file or library file. - name Deletes a module. -+ name Replaces a module by deleting it and Operator Action ──────────────────────────────────────────────────────────────────────────── -+ name Replaces a module by deleting it and appending an object file with the same name. * name Copies a module to a new object file. -* name Moves a module out of the library by copying it to a new object file and then deleting it. LINK The LINK utility combines object files into a single executable file or dynamic-link library. Command-Line Syntax LINK objfiles [, [exefile] [, [mapfile] [, [libraries] [, [deffile] ] ] ] ] [;] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /ALIGN: size Option name: /A[LIGNMENT]. Directs LINK to align segment data in a segmented executable file along the boundaries specified by size bytes, where size must be a power of two. /BATCH Option name: /B[ATCH]. Suppresses prompts for library or object files not found. /CO Option name: /CO[DEVIEW]. Adds symbolic Option Action ──────────────────────────────────────────────────────────────────────────── /CO Option name: /CO[DEVIEW]. Adds symbolic data and line numbers needed by the Microsoft CodeView debugger. This option is incompatible with the /EXEPACK option. /CPARM: number Option name: /CP[ARMAXALLOC]. Sets the program's maximum memory allocation to number of 16-byte paragraphs. /DOSSEG Option name: /DO[SSEG]. Orders segments in the default order used by Microsoft high-level languages. /DSALLOC Option name: /DS[ALLOCATE]. Directs LINK to load all data starting at the high end of the data segment. The /DSALLOC option is for assembly-language programs that create DOS .EXE files. Option Action ──────────────────────────────────────────────────────────────────────────── /EXEPACK Option name: /E[XEPACK]. Packs the executable file. The /EXEPACK option is incompatible with either /INCR or /CO. Do not use /EXEPACK on a Windows program. /FARCALL Option name: /F[ARCALLTRANSLATION]. Optimizes far calls. The /FARCALL option is on automatically when using /TINY. Use the /PACKC option with /FARCALL when linking for OS/2; /PACKC is not recommended with /FARCALL when linking for Windows. /HELP Option name: /HE[LP]. Calls QuickHelp for help on LINK. /HIGH Option name: /HI[GH]. Places the executable file as high in memory as Option Action ──────────────────────────────────────────────────────────────────────────── executable file as high in memory as possible. Use /HIGH with the /DSALLOC option. This option is for assembly-language programs that create DOS .EXE files. /INCR Option name: /INC[REMENTAL]. Prepares for incremental linking with ILINK. This option is incompatible with /EXEPACK and /TINY. /INFO Option name: /INF[ORMATION]. Displays to the standard output the phase of linking and names of object files being linked. /LINE Option name: /LI[NENUMBERS]. Adds source-file line numbers and associated addresses to the map file. The object file must be created with line numbers. Option Action ──────────────────────────────────────────────────────────────────────────── file must be created with line numbers. This option creates a map file even if mapfile is not specified. /MAP Option name: /M[AP]. Adds public symbols to the map file. /NOD[: libraryname] Option name: /NOD[EFAULTLIBRARYSEARCH]. Ignores the specified default library. Specify without libraryname to ignore all default libraries. /NOE Option name: /NOE[XTDICTIONARY]. Prevents LINK from searching extended dictionaries in libraries. Use /NOE when redefinition of a symbol causes error L2044. /NOFARCALL Option name: /NOF[ARCALLTRANSLATION]. Option Action ──────────────────────────────────────────────────────────────────────────── /NOFARCALL Option name: /NOF[ARCALLTRANSLATION]. Turns off far-call optimization. /NOI Option name: /NOI[GNORECASE]. Preserves case in identifiers. /NOLOGO Option name: /NOL[OGO]. Suppresses the LINK copyright message /NONULLS Option name: /NON[ULLSDOSSEG]. Orders segments as with the /DOSSEG option, but with no additional bytes at the beginning of the _TEXT segment (if defined). This option overrides /DOSSEG. /NOPACKC Option name: /NOP[ACKCODE]. Turns off code segment packing. /PACKC[: number] Option name: /PACKC[ODE]. Packs Option Action ──────────────────────────────────────────────────────────────────────────── /PACKC[: number] Option name: /PACKC[ODE]. Packs neighboring code segments together. Specify number bytes to set the maximum size for physical segments formed by /PACKC. /PACKD[: number] Option name: /PACKD[ATA]. Packs neighboring data segments together. Specify number bytes to set the maximum size for physical segments formed by /PACKD. This option is for OS/2 and Windows only. /PAUSE Option name: /PAU[SE]. Pauses during the link session for disk changes. /PM: type Option name: /PM[TYPE]. Specifies the type of Windows or OS/2 application where type is one of the following: PM Option Action ──────────────────────────────────────────────────────────────────────────── where type is one of the following: PM (or WINDOWAPI), VIO (or WINDOWCOMPAT), or NOVIO (or NOTWINDOWCOMPAT). /STACK: number Option name: /ST[ACK]. Sets the stack size to number bytes, from 1 byte to 64K. /TINY Option name: /T[INY]. Creates a tiny-model DOS program with a .COM extension instead of .EXE. Incompatible with /INCR. /? Option name: /?. Displays a brief summary of LINK command-line syntax. Note: Several rarely used options not listed above are described in online help. Environment Variables ╓┌────────────────┌──────────────────────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── INIT Specifies path for the TOOLS.INI file. LIB Specifies search path for library files. LINK Specifies default command-line options. TMP Specifies path for the VM.TMP file. MASM The MASM program converts command-line options from MASM style to ML style, adds options to maximize compatibility, and calls ML.EXE. Command-Line Syntax MASM [options] sourcefile [, [objectfile] [, [listingfile] [, [crossreferencefile] ] ] ] [;] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /A Orders segments alphabetically. Results in a warning. Ignored. /B Sets internal buffer size. Ignored. /C Creates a cross-reference file. Translated to /FR. /D Creates a Pass 1 listing. Ignored. /D symbol[ = value] Defines a symbol. Unchanged. /E Emulates floating-point instructions. Translated to /FPi. Option Action ──────────────────────────────────────────────────────────────────────────── Translated to /FPi. /H Lists command-line arguments. Translated to /help. /HELP Calls QuickHelp for help on the MASM driver. /I pathname Specifies an include path. Unchanged. /L Creates a normal listing. Translated to /Fl. /LA Lists all. Translated to /Fl and /Sa. /ML Treats names as case sensitive. Translated to /Cp. /MU Converts names to uppercase. Translated Option Action ──────────────────────────────────────────────────────────────────────────── /MU Converts names to uppercase. Translated to /Cu. /MX Preserves case on nonlocal names. Translated to /Cx. /N Suppresses table in listing file. Translated to /Sn. /P Checks for impure code. Use OPTION READONLY. Ignored. /S Orders segments sequentially. Results in a warning. Ignored. /T Enables terse assembly. Translated to /nologo. /V Enables verbose assembly. Ignored. Option Action ──────────────────────────────────────────────────────────────────────────── /V Enables verbose assembly. Ignored. /W0 Enables warning level 0. Unchanged. /W1 Enables warning level 1. Unchanged. /W2 Enables warning level 2. Unchanged. /X Lists false conditionals. Translated to /Sx. /Z Displays error lines on screen. Ignored. /ZD Generates line numbers for CodeView. Translated to /Zd. /ZI Generates symbols for CodeView. Translated to /Zi. Option Action ──────────────────────────────────────────────────────────────────────────── Environment Variables ╓┌────────────────┌──────────────────────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── INCLUDE Specifies default path for .INC files. MASM Specifies default command-line options. TMP Specifies path for temporary files. ML The ML program assembles and links one or more assembly-language source files. The command-line options are case sensitive. Command-Line Syntax ML [options] filename [ [options] filename]... [/link linkoptions] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /AT Enables tiny-memory-model support. Enables error messages for code constructs that violate the requirements for .COM format files. Note that this is not equivalent to the .MODEL TINY directive. /Bl filename Selects an alternate linker. Option Action ──────────────────────────────────────────────────────────────────────────── /c /Cp Preserves case of all user identifiers. /Cu Maps all identifiers to uppercase (default). /Cx Preserves case in public and extern symbols. /D symbol[ = value] Defines a text macro with the given name. If value is missing, it is blank. Multiple tokens separated by spaces must be enclosed in quotation marks. /EP Generates a preprocessed source listing (sent to STDOUT). See /Sf. Option Action ──────────────────────────────────────────────────────────────────────────── /F hexnum Sets stack size to hexnum bytes (this is the same as /link /STACK: number). The value must be expressed in hexadecimal notation. There must be a space between /F and hexnum. /Fb [ filename] Creates a bound executable file. /Fe filename Names the executable file. /Fl [ filename] Generates an assembled code listing. See /Sf. /Fm [ filename] Creates a linker map file. /Fo filename Names an object file. Option Action ──────────────────────────────────────────────────────────────────────────── /Fo filename Names an object file. /FPi Generates emulator fixups for floating-point arithmetic (mixed-language only). /Fr [ filename] Generates a source browser .SBR file. /FR [ filename] Generates an extended form of a source browser .SBR file. /Gc Specifies use of FORTRAN- or Pascal-style function calling and naming conventions. Same as OPTION LANGUAGE:PASCAL. /Gd Specifies use of C-style function calling and naming conventions. Same as OPTION LANGUAGE:C. Option Action ──────────────────────────────────────────────────────────────────────────── OPTION LANGUAGE:C. /H number Restricts external names to number significant characters. The default is 31 characters. /help Calls QuickHelp for help on ML. /I pathname Sets path for include file. A maximum of 10 /I options is allowed. /nologo Suppresses messages for successful assembly. /Sa Turns on listing of all available information. /Sf Adds first-pass listing to listing file. Option Action ──────────────────────────────────────────────────────────────────────────── /Sg Turns on listing of assembly-generated code. /Sl width Sets the line width of source listing in characters per line. Range is 60 to 255 or 0. Default is 0. Same as PAGE , width. /Sn Turns off symbol table when producing a listing. /Sp length Sets the page length of source listing in lines per page. Range is 10 to 255 or 0. Default is 0. Same as PAGE length. /Ss text Specifies text for source listing. Same as SUBTITLE text. Option Action ──────────────────────────────────────────────────────────────────────────── /St text Specifies title for source listing. Same as TITLE text. /Sx Turns on false conditionals in listing. /Ta filename Assembles source file whose name does not end with the .ASM extension. /w Same as /W0. /W level Sets the warning level: level 0, 1, 2, or 3. /WX Returns an error code if warnings are generated. Option Action ──────────────────────────────────────────────────────────────────────────── /Zd Generates line-number information in object file. /Zf Makes all symbols public. /Zi Generates CodeView information in object file. /Zm Enables M510 option for maximum compatibility with MASM 5.1. /Zp [ alignment] Packs structures on the specified byte boundary. The alignment may be 1, 2, or 4. /Zs Performs a syntax check only. /? Displays a brief summary of ML Option Action ──────────────────────────────────────────────────────────────────────────── /? Displays a brief summary of ML command-line syntax. QuickAssembler Support For compatibility with QuickAssembler makefiles, ML recognizes the following options: ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /a Orders segments alphabetically. In MASM 6.0, the .ALPHA directive must be used. Ignored. Option Action ──────────────────────────────────────────────────────────────────────────── Ignored. /Cl Equivalent to /Cp. /Ez Prints the source for error lines to the screen. This option is no longer supported and is ignored by MASM 6.0. /P1 Performs one-pass assembly. MASM 6.0 always performs a single pass through the source file. This option is ignored by MASM 6.0. /P2 Performs two-pass assembly. MASM 6.0 always performs a single pass through the source file. This option is ignored by MASM 6.0. /s Orders segments sequentially. In MASM Option Action ──────────────────────────────────────────────────────────────────────────── /s Orders segments sequentially. In MASM 6.0, the .SEQ directive must be used. Ignored. /Sq Equivalent to /Sl0 /Sp0. Environment Variables ╓┌────────────────┌──────────────────────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── INCLUDE Specifies search path for include files. ML Specifies default command-line options. TMP Specifies path for temporary files. NMAKE The NMAKE utility automates the process of compiling and linking project files. Command-Line Syntax NMAKE [options] [macros] [targets] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /A Executes all commands even if targets are not out-of-date. /C Suppresses the NMAKE copyright message and prevents nonfatal error or warning messages from being displayed. Option Action ──────────────────────────────────────────────────────────────────────────── messages from being displayed. /D Displays the modification time of each file when the times of targets and dependents are checked. /E Causes environment variables to override macro definitions within description files. /F filename Specifies filename as the name of the description file to use. If a dash (-) is entered instead of a filename, NMAKE reads the description file from the standard input device.If /F is not specified, NMAKE uses MAKEFILE as the description file. If MAKEFILE does not exist, NMAKE builds command-line targets using inference rules. Option Action ──────────────────────────────────────────────────────────────────────────── using inference rules. /HELP Calls QuickHelp for help on NMAKE. /I Ignores exit codes from commands in the description file. NMAKE continues executing the rest of the description file despite the errors. /N Displays but does not execute commands from the description file. /NOLOGO Suppresses the NMAKE copyright message. /P Displays all macro definitions, inference rules, target descriptions, and the . SUFFIXES list. /Q Checks modification times of Option Action ──────────────────────────────────────────────────────────────────────────── /Q Checks modification times of command-line targets (or first target in the description file if no command-line targets are specified). NMAKE returns a zero exit code if all such targets are up-to-date and a nonzero exit code if any target is out-of-date. Only preprocessing commands in the description file are executed. /R Ignores inference rules and macros that are defined in the TOOLS.INI file or are predefined. /S Suppresses display of commands as they are executed. /T Changes modification times of command-line targets (or first target in Option Action ──────────────────────────────────────────────────────────────────────────── command-line targets (or first target in the description file if no command-line targets are specified) to the current time. Only preprocessing commands in the description file are executed. The contents of target files are not modified. /X filename Sends all error output to filename, which can be either a file or a device. If a dash (-) is entered instead of a filename, the error output is sent to the standard output device. /Z Internal option for use by the Microsoft Programmer's WorkBench (PWB). /? Displays a brief summary of NMAKE command-line syntax. Option Action ──────────────────────────────────────────────────────────────────────────── command-line syntax. Environment Variable ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── INIT Specifies path for TOOLS.INI file, which may contain macros, inference rules, and description blocks. PWB (Programmer's WorkBench) The Microsoft Programmer's WorkBench (PWB) provides an integrated environment for developing programs in assembly language. The command-line options are case sensitive. Command-Line Syntax PWB [options] [files] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /D[ init] Prevents PWB from examining initialization files, where init is one or more of the following characters: A Disable autoload extensions (including language-specific extensions and online help) Option Action ──────────────────────────────────────────────────────────────────────────── and online help) S Ignore CURRENT.STS T Ignore TOOLS.INI If the /D option does not include an init character, it is equivalent to specifying /DAST (all files /e cmdstr Executes the command or sequence of commands at start-up. The entire cmdstr argument must be placed in double quotation marks if it contains a space. If cmdstr contains literal double quotation marks, place a backslash (\) in front of each double quotation mark. To include a literal backslash in the Option Action ──────────────────────────────────────────────────────────────────────────── To include a literal backslash in the command string, use double backslashes (\\). /m mark Moves the cursor to the specified mark instead of moving it to the last known position. The mark can be a line number. /P[ init] Specifies a program list for PWB to read, where init can be F file Read a foreign program list (one not created using PWB). L Read the last program list. Use this option to start PWB in the same state you left it. P file Read a PWB program list. Option Action ──────────────────────────────────────────────────────────────────────────── P file Read a PWB program list. /r Starts PWB in no-edit mode. Functions that modify files are disallowed. [ [/t] file...] Loads the specified file at start-up. The file specification can contain wildcards. If multiple files are specified, PWB loads only the first file. When the Exit function is invoked, PWB saves the current file and loads the next file in the list. Files specified with /t are temporary; PWB does not add them to the file history on the File menu. No other options can follow /t on the command line. Each temporary file must be specified in a separate /t option. Option Action ──────────────────────────────────────────────────────────────────────────── be specified in a separate /t option. /? Displays a brief summary of PWB command-line syntax. Environment Variables ╓┌────────────┌──────────────────────────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── HELPFILES Specifies path of help files or list of help filenames. INIT Specifies path for TOOLS.INI and CURRENT.STS files. TMP Specifies path for temporary files. PWBRMAKE PWBRMAKE converts the .SBR files created by the assembler into database .BSC files that can be read by the Microsoft Programmer's WorkBench (PWB) Source Browser. The command-line options are case sensitive. Command-Line Syntax PWBRMAKE [options] sbrfiles Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /Ei filename/Ei ( filename...) Excludes the contents of the specified include files from the database. To specify multiple filenames, separate them with spaces and enclose the list in parentheses. Option Action ──────────────────────────────────────────────────────────────────────────── /Em Excludes symbols in the body of macros. Use /Em to include only macro names. /Es Excludes from the database every include file specified with an absolute pathname or found in an absolute path specified in the INCLUDE environment variable. /HELP Calls QuickHelp for help on PWBRMAKE. /Iu Includes unreferenced symbols. /n Forces a nonincremental build and prevents truncation of .SBR files. /o filename Specifies a name for the database file. Option Action ──────────────────────────────────────────────────────────────────────────── /o filename Specifies a name for the database file. /v Displays verbose output. /? Displays a brief summary of PWBRMAKE command-line syntax. QuickHelp The QuickHelp utility displays online help files. All MASM reserved words and error messages can be used for topic. Command-Line Syntax QH [options] [topic] Options ╓┌─────────────────────────────────┌─────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /d filename Specifies either a specific database name or a path where the databases are found. /l number Specifies the number of lines the QuickHelp window should occupy. /m number Changes the screen mode to display the specified number of lines, where number is in the range 25 to 60. /p filename Sets the name of the paste file. /pa [ filename] Specifies that pasting operations are appended to the current paste file (rather than overwriting the file). Option Action ──────────────────────────────────────────────────────────────────────────── (rather than overwriting the file). /q Prevents the version box from being displayed when QuickHelp is installed as a keyboard monitor. /r command Specifies the command that QuickHelp should execute when the right mouse button is pressed. The command can be one of the following letters: l Display last topic i Display history of help topics w Hide window b Display previous topic Option Action ──────────────────────────────────────────────────────────────────────────── e Find next topic t Display contents /s Specifies that clicking the mouse above or below the scroll box causes QuickHelp to scroll by lines rather than by pages. /sg number Specifies the number of screen groups that QuickHelp should monitor, where number is in the range 1 to 12. This option is valid only when QuickHelp is detached from an OS/2 protected-mode screen group. /t name Directs QuickHelp to copy the specified section of the given topic to the current paste file and exit. The name Option Action ──────────────────────────────────────────────────────────────────────────── current paste file and exit. The name may be All Paste the entire topic Syntax Paste the syntax only Example Paste the example only If the topic is not found, QuickHelp returns an exit code of 1. /u Specifies that QuickHelp is being run by a utility. If the topic specified on the command line is not found, QuickHelp immediately exits with an exit code of 3. Environment Variables ╓┌────────────┌──────────────────────────────────────────────────────────────╖ Variable Description ──────────────────────────────────────────────────────────────────────────── HELPFILES Specifies path of help files or list of help filenames. QH Specifies default command-line options. TMP Specifies directory of default paste file. RM The RM utility moves a file to a hidden DELETED subdirectory of the directory containing the file. Use the UNDEL utility to recover the file and the EXP utility to expunge the hidden file. Command-Line Syntax RM [options] [files] Options ╓┌──────────────┌────────────────────────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /F Deletes read-only files without prompting. /HELP Calls QuickHelp for help on RM. /I Inquires for permission before removing each file. /K Keeps read-only files without prompting. /R directory Recurses into subdirectories of the specified directory. /? Displays a brief summary of RM command-line syntax. UNDEL The UNDEL utility moves a file from a hidden DELETED subdirectory to the parent directory. UNDEL is used along with EXP and RM to manage backup files. Command-Line Syntax UNDEL [{option | files}] Options ╓┌──────────┌────────────────────────────────────────────────────────────────╖ Option Action ──────────────────────────────────────────────────────────────────────────── /HELP Calls QuickHelp for help on UNDEL. /? Displays a brief summary of UNDEL command-line syntax. Cross-References Topical Cross-Reference for Directives Simplified Segment .MODEL .STARTUP .EXIT .CODE .STACK .DATA .DATA? .FARDATA .FARDATA? .CONST .DOSSEG Segment SEGMENT ENDS GROUP ASSUME END .ALPHA .DOSSEG .SEQ Conditional Assembly IF IFE IFB/IFNB IFDEF/IFNDEF IFDIF/IFDIFI IFIDN/IFIDNI ELSE ENDIF Macros MACRO LOCAL PURGE GOTO ENDM EXITM Data Allocation BYTE/SBYTE WORD/SWORD DWORD/SDWORD FWORD QWORD TBYTE LABEL ALIGN EVEN ORG REAL4 REAL8 REAL10 Code Labels LABEL ALIGN EVEN ORG Scope PUBLIC EXTERNDEF EXTERN COMM INCLUDELIB Structure and Record RECORD STRUCT UNION ENDS TYPEDEF String CATSTR SIZESTR SUBSTR INSTR Equates EQU = TEXTEQU Repeat Blocks REPEAT WHILE FOR FORC ENDM GOTO Conditional Control Flow .IF .ELSE .ELSEIF .ENDIF .WHILE .ENDW .REPEAT .UNTIL/ .UNTILCXZ .BREAK .CONTINUE Listing Control TITLE SUBTITLE PAGE .LIST .NOLIST .LISTIF .NOLISTIF .TFCOND .LISTMACROALL .NOLISTMACRO .LISTMACRO .CREF .NOCREF .LISTALL Conditional Error .ERR .ERRE .ERRNZ .ERRB .ERRNB .ERRDEF .ERRNDEF .ERRDIF/.ERRDIFI .ERRIDN/.ERRIDNI Processor .8086 .486 .186 .486P .286 .8087 .286P .287 .386 .387 .386P .NO87 Procedures PROC ENDP PROTO INVOKE USES Miscellaneous OPTION COMMENT ECHO .RADIX END PUSHCONTEXT POPCONTEXT INCLUDE INCLUDELIB ASSUME Topical Cross-Reference for Symbols Segment Information @code @CodeSize @CurSeg @data @DataSize @fardata @fardata? @Model @stack @WordSize Macro Functions @CatStr @InStr @SizeStr @SubStr Environment Information @Cpu @Environ @Interface @Version Date and Time Information @Date @Time File Information @FileCur @FileName @Line Miscellaneous $ ? @@: @B @F Topical Cross-Reference for Operators Arithmetic + MOD - . * [] / Macro <> % ! & ;; Relational EQ GE NE LT GT LE Logical and ShiftAND OR XOR NOT SHL SHR Record MASK WIDTH Segment : SEG OFFSET LROFFSET Type HIGH HIGHWORD LOW LOWWORD PTR SHORT SIZE SIZEOF LENGTH LENGTHOF THIS TYPE OPATTR Control Flow ! = = != >= && <= || > & < Miscellaneous ; : DUP :: " " ' ' CARRY? OVERFLOW? PARITY? SIGN? ZERO? Directives name = expression Assigns the numeric value of expression to name. The symbol may be redefined later. .186 Enables assembly of instructions for the 80186 processor; disables assembly of instructions introduced with later processors. Also enables 8087 instructions. .286 Enables assembly of nonprivileged instructions for the 80286 processor; disables assembly of instructions introduced with later processors. Also enables 80287 instructions. .286P Enables assembly of all instructions (including privileged) for the 80286 processor; disables assembly of instructions introduced with later processors. Also enables 80287 instructions. .287 Enables assembly of instructions for the 80287 coprocessor; disables assembly of instructions introduced with later coprocessors. .386 Enables assembly of nonprivileged instructions for the 80386 processor; disables assembly of instructions introduced with later processors. Also enables 80387 instructions. .386P Enables assembly of all instructions (including privileged) for the 80386 processor; disables assembly of instructions introduced with later processors. Also enables 80387 instructions. .387 Enables assembly of instructions for the 80387 coprocessor. .486 Enables assembly of nonprivileged instructions for the 80486 processor. .486P Enables assembly of all instructions (including privileged) for the 80486 processor. .8086 Enables assembly of 8086 instructions (and the identical 8088 instructions); disables assembly of instructions introduced with later processors. Also enables 8087 instructions. This is the default mode for processors. .8087 Enables assembly of 8087 instructions; disables assembly of instructions introduced with later coprocessors. This is the default mode for coprocessors. ALIGN [ number] Aligns the next variable or instruction on a byte that is a multiple of number. .ALPHA Orders segments alphabetically. ASSUME segregister : name [ , segregister : name]... ASSUME dataregister : type [ , dataregister : type]... ASSUME register :ERROR [ , register :ERROR]... ASSUME [ register :] NOTHING [ , register :NOTHING]... Enables error-checking for register values. After an ASSUME is put into effect, the assembler watches for changes to the values of the given registers. ERROR generates an error if the register is used at all. NOTHING assumptions in one statement. .BREAK [ .IF condition] Generates code to terminate a .WHILE or .REPEAT block if condition is true. [ name] BYTE initializer [ , initializer]... Allocates and optionally initializes a byte of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. name CATSTR [ textitem1 [ , textitem2]...] Concatenates text items. Each text item can be a literal string, a constant preceded by a %, or the string returned by a macro function. .CODE [ name] When used with .MODEL, indicates the start of a code segment called name (the default segment name is _TEXT for tiny, small, compact, and flat models, or module_TEXT for other models). COMM definition [ , definition]... Creates a communal variable with the attributes specified in definition. Each definition has the following form: [ langtype] [ NEAR | FAR] label : type[ : count] The label is the name of the variable. The type can be any type specifier ( BYTE, WORD, etc.) or an integer specifying the number of bytes. The count specifies the number of data objects (one is the default). COMMENT delimiter [ text] [ text] [ text] delimiter [ text] Treats all text between or on the same line as the delimiters as a comment. .CONST When used with .MODEL, starts a constant data segment (with segment name CONST). This segment has the read-only attribute. .CONTINUE [ .IF condition] Generates code to jump to the top of a .WHILE or .REPEAT block if condition is true. .CREF Enables listing of symbols in the symbol portion of the symbol table and browser file. .DATA When used with .MODEL, starts a near data segment for initialized data (segment name _DATA). .DATA? When used with .MODEL, starts a near data segment for uninitialized data (segment name _BSS). .DOSSEG Orders the segments according to the DOS segment convention: CODE first, then segments not in DGROUP, and then segments in DGROUP. The segments in DGROUP follow this order: segments not in BSS or STACK, then BSS segments, and finally STACK segments. Primarily used for ensuring CodeView support in MASM stand-alone programs. Same as DOSSEG. DOSSEG Identical to . DOSSEG, which is the preferred form. DB Can be used to define data like BYTE. DD Can be used to define data like DWORD. DF Can be used to define data like FWORD. DQ Can be used to define data like QWORD. DT Can be used to define data like TBYTE. DW Can be used to define data like WORD. [ name] DWORD initializer [ , initializer]... Allocates and optionally initializes a doubleword (4 bytes) of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. ECHO message Displays message to the standard output device (by default, the screen). Same as %OUT. .ELSE See .IF. ELSE Marks the beginning of an alternate block within a conditional block. See IF. END [ address] Marks the end of a module and, optionally, sets the program entry point to address. .ENDIF See .IF. ENDIF See IF. ENDM Terminates a macro or repeat block. See MACRO, FOR, FORC, REPEAT, or WHIL name ENDP Marks the end of procedure name previously begun with PROC. See PROC. name ENDS Marks the end of segment, structure, or union name previously begun with SEG .ENDW See .WHILE. name EQU expression Assigns numeric value of expression to name. The name cannot be redefined later. name EQU < text > Assigns specified text to name. The name can be assigned a different text .ERR [ message] Generates an error. .ERRB < textitem > [ , message] Generates an error if textitem is blank. .ERRDEF name [ , message] Generates an error if name is a previously defined label, variable, or symbol. .ERRDIF[ I] < textitem1 >, < textitem2 > [ , message] Generates an error if the text items are different. If I is given, the comparison is case insensitive. .ERRE expression [ , message] Generates an error if expression is false (0). .ERRIDN[ I] < textitem1 >, < textitem2 > [ , message] Generates an error if the text items are identical. If I is given, the comparison is case insensitive. .ERRNB < textitem > [ , message] Generates an error if textitem is not blank. .ERRNDEF name [ , message] Generates an error if name has not been defined. .ERRNZ expression [ , message] Generates an error if expression is true (nonzero). EVEN Aligns the next variable or instruction on an even byte. .EXIT [ expression] Generates termination code. Returns optional expression to shell. EXITM [ expression] Terminates expansion of the current repeat or macro block and begins assembly of the next statement outside the block. In a macro function, expression is the value returned. EXTERN [ langtype] name [ ( altid )] : type [ , [ langtype] name [ ( altid )] : type]... Defines one or more external variables, labels, or symbols called name whose type is type. The type can be ABS, which imports name as a constant. Same as EXTRN. EXTERNDEF [ langtype] name : type [ , [ langtype] name : type]... Defines one or more external variables, labels, or symbols called name whose type is type. If name is defined in the module, it is treated as PUBLIC. If name is referenced in the module, it is treated as EXTERN. If name is not referenced, it is ignored. The type can be ABS, which imports name as a constant. Normally used in include files. EXTRN See EXTERN. .FARDATA [ name] When used with .MODEL, starts a far data segment for initialized data (segment name FAR_DATA or name). .FARDATA? [ name] When used with .MODEL, starts a far data segment for uninitialized data (segment name FAR_BSS or name). FOR parameter [ :REQ | := default] , < argument [ , argument]... > statements ENDM Marks a block that will be repeated once for each argument, with the current argument replacing parameter on each repetition. Same as IRP. FORC parameter , < string > statements ENDM Marks a block that will be repeated once for each character in string, with the current character replacing parameter on each repetition. Same as IRPC. [ name] FWORD initializer [ , initializer]... Allocates and optionally initializes 6 bytes of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. GOTO macrolabel Transfers assembly to the line marked : macrolabel. GOTO is permitted only inside MACRO, FOR, FORC, REPEAT, and WHILE blocks. The label must be the only directive on the line and must be preceded by a leading colon. name GROUP segment [ , segment]... Add the specified segments to the group called name. .IF condition1 statements [ .ELSEIF condition2 statements] [ .ELSE statements] .ENDIF Generates code that tests condition1 (for example, AX > 7) and executes the statements if that condition is true. If an .ELSE follows, its statements are executed if the original condition was false. Note: The conditions are evaluated at run time. IF expression1 ifstatements [ ELSEIF expression2 elseifstatements] [ ELSE elsestatements] ENDIF Grants assembly of ifstatements if expression1 is true (nonzero) or elseifstatements if expression1 is false (0) and expression2 is true. The following directives may be substituted for ELSEIF: ELSEIFB, ELSEIFDEF, ELSEIFDIF, ELSEIFDIFI, ELSEIFE, ELSEIFIDN, ELSEIFIDNI, ELSEIFNB, and ELS is false. Note: The expressions are evaluated at assembly time. IFB textitem Grants assembly if textitem is blank. See IF for complete syntax. IFDEF name Grants assembly if name is a previously defined label, variable, or symbol. See IF for complete syntax. IFDIF[ I] textitem1 , textitem2 Grants assembly if the text items are different. If I is given, the comparison is case insensitive. See IF for complete syntax. IFE expression Grants assembly if expression is false (0). See IF for complete syntax. IFIDN[ I] textitem1 , textitem2 Grants assembly if the text items are identical. If I is given, the comparison is case insensitive. See IF for complete syntax. IFNB textitem Grants assembly if textitem is not blank. See IF for complete syntax. IFNDEF name Grants assembly if name has not been defined. See IF for complete syntax. INCLUDE filename Inserts source code from the source file given by filename into the current source file during assembly. The filename must be enclosed in angle brackets if it includes a backslash, semicolon, greater-than symbol, less-than symbol, single quotation mark, or double quotation mark. INCLUDELIB libraryname Informs the linker that the current module should be linked with libraryname. The libraryname must be enclosed in angle brackets if it includes a backslash, semicolon, greater-than symbol, less-than symbol, single quotation mark, or double quotation mark. name INSTR [ position ,] textitem1 , textitem2 Finds the first occurrence of textitem2 in textitem1. The starting position is optional. Each text item can be a literal string, a constant preceded by a %, or the string returned by a macro function. INVOKE expression [ , arguments] Calls the procedure at the address given by expression, passing the arguments on the stack or in registers according to the standard calling conventions of the language type. Each argument passed to the procedure may be an expression, a register pair, or an address expression (an expression preceded by ADDR). IRP See FOR. IRPC See FORC. name LABEL type Creates a new label by assigning the current location-counter value and the given type to name. name LABEL [ NEAR | FAR | PROC] PTR [ type] Creates a new label by assigning the current location-counter value and the given type to name. .LALL See .LISTMACROALL. .LFCOND See .LISTIF. .LIST Starts listing of statements. This is the default. .LISTALL Starts listing of all statements. Equivalent to the combination of .LIST, .LISTIF, and .LISTMACROALL. .LISTIF Starts listing of statements in false conditional blocks. Same as .LFCOND. .LISTMACRO Starts listing of macro expansion statements that generate code or data. This is the default. Same as .XALL. .LISTMACROALL Starts listing of all statements in macros. Same as .LALL. LOCAL localname [ , localname]... Within a macro, LOCAL defines labels that are unique to each instance of the macro. LOCAL label [ [ count ] ] [ : type] [ , label [ [ count ] ] [ type] ]... Within a procedure definition ( PROC), LOCAL creates stack-based variables that exist for the duration of the procedure. The label may be a simple variable or an array containing count elements. name MACRO [ parameter [ :REQ | := default | :VARARG] ]... statements ENDM [ value] Marks a macro block called name and establishes parameter placeholders for arguments passed when the macro is called. A macro function returns value to the calling statement. .MODEL memorymodel [ , langtype] [ , ostype] [ , stackoption] Initializes the program memory model. The memorymodel may be TINY, SMALL, COMPACT, MEDIUM, LARGE, HUGE, or FLAT. The langtype may be C, BASIC, FORTRAN, PASCAL, SYSCALL, or STDCALL. The ostype may be OS_DOS or OS_OS2. The stackoption may be NEARSTACK or FARSTACK. NAME modulename Ignored in version 6.0. .NO87 Disallows assembly of all floating-point instructions. .NOCREF [ name[ , name]...] Suppresses listing of symbols in the symbol table and browser file. If names are specified, only the given names are suppressed. Same as .XCREF. .NOLIST Suppresses program listing. Same as .XLIST. .NOLISTIF Suppresses listing of conditional blocks whose condition evaluates to false (0). This is the default. Same as .SFCOND. .NOLISTMACRO Suppresses listing of macro expansions. Same as .SALL. OPTION optionlist Enables and disables features of the assembler. Available options include CASEMAP, DODD DOTNAME, NODOTNAME, EPILOGUEEE EMULATOR, NOEMULATOR, EPILOGUE, EXPR16, EXPR32, LANGUAGE, LJMP, NOLJMP, M510, NOM510, NOKEYWORD, NOSIGNEXTEND, OFFSET, OLDMACROS, NOOLDMACROS, OLDSTRUCTS, NOOLDSTRUCTS, PROC, PROLOGUE, READONLY, NOREADONLY, SCOPED, NOSCOPED, and SEGMENT. ORG expression Sets the location counter to expression. %OUT See ECHO. PAGE [ [ length] , width] Sets line length and character width of the program listing. If no arguments are given, generates a page break. PAGE + Increments the section number and resets the page number to 1. POPCONTEXT context Restores part or all of the current context (saved by the PUSHCONTEXT directive). The context can be ASSUMES, RADIX, LISTING, CPU, or ALL. label PROC [ distance] [ langtype] [ visibility] [ < prologuearg >] [ USES reglist] [ , parameter [ : tag] ]... statements label ENDP Marks start and end of a procedure block called label. The statements in the block can be called with the CALL instruction or INVOKE directive. label PROTO [ distance] [ langtype] [ , [ parameter] : tag]... Prototypes a function. PUBLIC [ langtype] name [ , [ langtype] name]... Makes each variable, label, or absolute symbol specified as name available to all other modules in the program. PURGE macroname [ , macroname]... Deletes the specified macros from memory. PUSHCONTEXT context Saves part or all of the current context: segment register assumes, radix value, listing and cref flags, or processor/coprocessor values. The context can be ASSUMES, RADIX, LISTING, CPU, or ALL. [ name] QWORD initializer [ , initializer]... Allocates and optionally initializes 8 bytes of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. .RADIX expression Sets the default radix, in the range 2 to 16, to the value of expression. name REAL4 initializer [ , initializer]... Allocates and optionally initializes a single-precision (4-byte) floating-point number for each initializer. name REAL8 initializer [ , initializer]... Allocates and optionally initializes a double-precision (8-byte) floating-point number for each initializer. name REAL10 initializer [ , initializer]... Allocates and optionally initializes a 10-byte floating-point number for each initializer. recordname RECORD fieldname : width [ = expression] [ , fieldname : width [ = expression] ]... Declares a record type consisting of the specified fields. The fieldname names the field, width specifies the number of bits, and expression gives its initial value. .REPEAT statements .UNTIL condition Generates code that repeats execution of the block of statements until condition becomes true. .UNTILCXZ, which becomes true when CX is zero, may be substituted for .UNTIL. The condition is optional with .UNTILCXZ. REPEAT expression statements ENDM Marks a block that is to be repeated expression times. Same as REPT. REPT See REPEAT. .SALL See .NOLISTMACRO. name SBYTE initializer [ , initializer]... Allocates and optionally initializes a signed byte of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. name SDWORD initializer [ , initializer]... Allocates and optionally initializes a signed doubleword (4 bytes) of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. name SEGMENT [ READONLY] [ align] [ combine] [ use] [ ' class '] statements name ENDS Defines a program segment called name having segment attributes align (BYTE AT address, PRIVATE), use ( USE16, USE32, FLAT), and class. .SEQ Orders segments sequentially (the default order). .SFCOND See .NOLISTIF. name SIZESTR textitem Finds the size of a text item. .STACK [ size] When used with .MODEL, defines a stack segment (with segment name STACK). The optional size specifies the number of bytes for the stack (default 1,024). The .STACK directive automatically closes the stack statement. .STARTUP Generates program start-up code. STRUC See STRUCT. name STRUCT [ alignment] [ , NONUNIQUE] fielddeclarations name ENDS Declares a structure type having the specified fielddeclarations. Each field must be a valid data definition. Same as STRUC. STRUC STRUCT name SUBSTR textitem , position [ , length] Returns a substring of textitem, starting at position. The textitem can be a literal string, a constant preceded by a %, or the string returned by a macro function. SUBTITLE text Defines the listing subtitle. Same as SUBTTL. SUBTTL See SUBTITLE. name SWORD initializer [ , initializer]... Allocates and optionally initializes a signed word (2 bytes) of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. [ name] TBYTE initializer [ , initializer]... Allocates and optionally initializes 10 bytes of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. name TEXTEQU [ textitem] Assigns textitem to name. The textitem can be a literal string, a constant preceded by a %, or the string returned by a macro function. .TFCOND Toggles listing of false conditional blocks. TITLE text Defines the program listing title. name TYPEDEF type Defines a new type called name, which is equivalent to type. name UNION [ alignment] [ , NONUNIQUE] fielddeclarations [ name] ENDS Declares a union of one or more data types. The fielddeclarations must be valid data definitions. Omit the ENDS name label on nested UNION definitions. .UNTIL See .REPEAT. .UNTILCXZ See .REPEAT. .WHILE condition statements .ENDW Generates code that executes the block of statements while condition remains true. WHILE expression statements ENDM Repeats assembly of block statements as long as expression remains true. [ name] WORD initializer [ , initializer]... Allocates and optionally initializes a word (2 bytes) of storage for each initializer. Can also be used as a type specifier anywhere a type is legal. .XALL See .LISTMACRO. .XCREF See .NOCREF. .XLIST See .NOLIST. Predefined Symbols $ The current value of the location counter. ? In data declarations, a value that the assembler allocates but does not initialize. @@: Defines a local code label. Overrides any previous @@: labels. See @B and @F. The location of the previous @@: label. @CatStr( string1 [ , string2...] ) Macro function that concatenates one or more strings. Returns a string. @code The name of the code segment (text macro). @CodeSize 0 for TINY, SMALL, COMPACT, and FLAT models, and 1 for MEDIUM, LARGE, and HUGE models (numeric equate). @Cpu A bit mask specifying the processor mode (numeric equate). @CurSeg The name of the current segment (text macro). @data The name of the default data group. Evaluates to DGROUP for all models except FLAT. Evaluates to FLAT under the FLAT memory model (text macro). @DataSize 0 for TINY, SMALL, MEDIUM, and FLAT models, 1 for COMPACT and LARGE models, and 2 for HUGE model (numeric equate). @Date The system date in the format mm/dd/yy (text macro). @Environ( envvar ) Value of environment variable envvar (macro function). @F The location of the next @@: label. @fardata The name of the segment defined by the .FARDATA directive (text macro). @fardata? The name of the segment defined by the .FARDATA? directive (text macro). @FileCur The name of the current file (text macro). @FileName The base name of the main file being assembled (text macro). @InStr( [ position] , string1 , string2 ) Macro function that finds the first occurrence of string2 in string1. The starting position within string1 is optional. Returns an integer (0 if string2 is not found). @Interface Information about the language parameters (numeric equate). @Line The source line number in the current file (numeric equate). @Model 1 for TINY model, 2 for SMALL model, 3 for COMPACT model, 4 for MEDIUM model, 5 for LARGE model, 6 for HUGE model, and 7 for FLAT model (numeric equate). @SizeStr( string ) Macro function that returns the length of the given string. Returns an integer. @SubStr( string , position [ , length] ) Macro function that returns a substring starting at position. @stack DGROUP for near stacks or STACK for far stacks (text macro). @Time The system time in 24-hour hh:mm:ss format (text macro). @Version 600 in MASM 6.0 (text macro). @WordSize 2 for a 16-bit segment or 4 for a 32-bit segment (numeric equate). Operators expression1 + expression2 Returns expression1 plus expression2. expression1 - expression2 Returns expression1 minus expression2. expression1 * expression2 Returns expression1 times expression2. expression1 / expression2 Returns expression1 divided by expression2. -expression Reverses the sign of expression. [expression1] [expression2 ] Returns expression1 plus [expression2 ]. segment : expression Overrides the default segment of expression with segment. The segment can be a segment register, group name, segment name, or segment expression. The e expression . field [ . field]... Returns expression plus the offset of field within its structure or union. [register ]. field [ . field]... Returns value at the location pointed to by register plus the offset of field within its structure or union. <text > Treats text as a single literal element. "text" Treats "text" as a string. 'text' Treats 'text' as a string. !character Treats character as a literal character rather than as an operator or symbol. ;text Treats text as a comment. ;;text Treats text as a comment that will not be listed in expanded macros. %expression Treats the value of expression in a macro argument as text. ¶meter & Replaces parameter with its corresponding argument value. ABS See the EXTERNDEF directive. ADDR See the INVOKE directive. expression1 AND expression2 Returns the result of a bitwise Boolean AND done on expression1 and expressio count DUP (initialvalue [ , initialvalue]...) Specifies count number of declarations of initialvalue. expression1 EQ expression2 Returns true (-1) if expression1 equals expression2, or returns false (0) if it does not. expression1 GE expression2 Returns true (-1) if expression1 is greater than or equal to expression2, or returns false (0) if it is not. expression1 GT expression2 Returns true (-1) if expression1 is greater than expression2, or returns false (0) if it is not. HIGH expression Returns the high byte of expression. HIGHWORD expression Returns the high word of expression. expression1 LE expression2 Returns true (-1) if expression1 is less than or equal to expression2, or returns false (0) if it is not. LENGTH variable Returns the number of data items in variable created by the first initializer. LENGTHOF variable Returns the number of data objects in variable. LOW expression Returns the low byte of expression. LOWWORD expression Returns the low word of expression. LROFFSET expression Returns the offset of expression. Same as OFFSET, but it generates a loader resolved offset, which allows Windows to relocate code segments. expression1 LT expression2 Returns true (-1) if expression1 is less than expression2, or returns false (0) if it is not. MASK {recordfieldname | record} Returns a bit mask in which the bits in recordfieldname or record are set and all other bits are cleared. expression1 MOD expression2 Returns the remainder of dividing expression1 by expression2. expression1 NE expression2 Returns true (-1) if expression1 does not equal expression2, or returns false (0) if it does. NOT expression Returns expression with all bits reversed. OFFSET expression Returns the offset of expression. OPATTR expression Returns a word defining the mode and scope of expression. The low byte is identical to the byte returned by .TYPE. The high byte contains additional information. expression1 OR expression2 Returns the result of a bitwise OR done on expression1 and expression2. type PTR expression Forces the expression to be treated as having the specified type. [distance] PTR type Specifies a pointer to type. SEG expression Returns the segment of expression. expression SHL count Returns the result of shifting the bits of expression left count number of bits. SHORT label Sets the type of label to short. All jumps to label must be short (within the range -128 to +127 bytes from the jump instruction to label). expression SHR count Returns the result of shifting the bits of expression right count number of bits. SIZE variable Returns the number of bytes in variable allocated by the first initializer. SIZEOF {variable | type} Returns the number of bytes in variable or type. THIS type Returns an operand of specified type whose offset and segment values are equal to the current location-counter value. .TYPE expression See OPATTR. TYPE expression Returns the type of expression. WIDTH {recordfieldname | record} Returns the width in bits of the current recordfieldname or record. expression1 XOR expression2 Returns the result of a bitwise Boolean XOR done on expression1 and expression2. Run-Time Operators The following operators are used only within .IF, .WHILE, or .REPEAT blocks and are evaluated at run time, not at assembly time: expression1 == expression2 Is equal to. expression1 != expression2 Is not equal to. expression1 > expression2 Is greater than. expression1 >= expression2 Is greater than or equal to. expression1 < expression2 Is less than. expression1 <= expression2 Is less than or equal to. expression1 || expression2 Logical OR. expression1 && expression2 Logical AND. expression1 & expression2 Bitwise AND. ! expression Logical negation. CARRY? Carry (C) processor flag. OVERFLOW? Overflow (O) processor flag. PARITY? Parity (P) processor flag. SIGN? Sign (S) processor flag. ZERO? Zero (Z) processor flag. Processor Topical Cross-Reference for Processor Data Transfer MOV MOVS MOVSX MOVZX XCHG LODS STOS LEA LDS/LES LFS/LGS/LSS XLAT/XLATB BSWAP# CMPXCHG# XADD# Stack PUSH PUSHF PUSHA* POP POPF POPA* ENTER* LEAVE* Input/Output IN INS* OUT OUTS* Type Conversion CBW CWD CWDE CDQ BSWAP# Flag CLC CLD CLI CMC STC STD STI POPF PUSHF LAHF SAHF String MOVS LODS STOS SCAS CMPS INS* OUTS* REP REPE/REPZ REPNE/REPNZ Arithmetic ADD ADC INC SUB SBB DEC NEG IMUL MUL DIV IDIV XADD# Bit Operations AND OR XOR NOT ROL ROR RCL RCR SHL/SAL SHR SAR SHLD SHRD BSF BSR BT BTC BTR BTS Compare CMP CMPS TEST BT BTC BTR BTS CMPXCHG# Unconditional Transfer CALL INT IRET RET RETN/RETF JMP Loop LOOP LOOPE/LOOPZ LOOPNE/LOOPNZ JCXZ/JECXZ Conditional Transfer JB/JNAE JAE/JNB JBE/JNA JA/JNBE JE/JZ JNE/JNZ JL/JNGE JGE/JNL JLE/JNG JG/JNLE JS JNS JC JNC JO JNO JP/JPE JNP/JPO JCXZ/JECXZ INTO BOUND* Conditional Set SETB/SETNAE SETAE/SETNB SETBE/SETNA SETA/SETNBE SETE/SETZ SETNE/SETNZ SETL/SETNGE SETGE/SETNL SETLE/SETNG SETG/SETNLE SETS SETNS SETC SETNC SETO SETNO SETP/SETPE SETNP/SETPO BCD Conversion AAA AAS AAM AAD DAA DAS Processor Control NOP WAIT LOCK HLT Process Control ARPL CLTS LAR LGDT/LIDT/LLDT LMSW LSL LTR SGDT/SIDT/SLDT SMSW STR VERR VERW MOV special INVD# INVLPG# WBINVD# Interpreting Processor Instructions This section provides an alphabetical reference to the instructions for the 8086, 8088, 80286, 80386, and 80486 processors. Figure 1 gives a key to each element of the reference. Flags The first row of the display has a one-character abbreviation for the flag name. Only the flags common to all processors are shown. O Overflow T Trap A Auxiliary carry D Direction S Sign P Parity I Interrupt Z Zero C Carry The second line has codes indicating how the flag can be affected. 1 Sets the flag 0 Clears the flag ? May change the flag, but the value is not predictable blank No effect on the flag +- Modifies according to the rules associated with the flag Syntax Each encoding variation may have different syntaxes corresponding to different addressing modes. The following abbreviations are used: reg A general-purpose register of any size segreg One of the segment registers: DS, ES, SS, or CS (also FS or GS on the 80386/486) accum An accumulator register of any size: AL or AX (also EAX on the 80386/486) mem A direct or indirect memory operand of any size label A labeled memory location in the code segment src,dest A source or destination memory operand used in a string operation immed A constant operand In some cases abbreviations have numeric suffixes to specify that the operand must be a particular size. For example, reg16 means that only a 16-bit (word) register is accepted. Examples One or more examples are shown for each syntax. Their position is not related to the clock speeds in the right column. Clock Speeds Column 3 shows the clock speeds for each processor. Sometimes an instruction may have more than one clock speed. Multiple speeds are separated by commas. If several speeds are part of an expression, they are enclosed in parentheses. The following abbreviations are used to specify variations: EA Effective address. This applies only to the 8088 and 8086 processors, described in the next section. b,w,d Byte, word, or doubleword operands. pm Protected mode. n Iterations. Repeated instructions may have a base number of clocks pl number of clocks for each iteration. For example, 8+4n means eight clocks plus four clocks for each iteration. noj No jump. For conditional jump instructions, noj indicates the speed i condition is false and the jump is not taken. m Next instruction components. Some control transfer instructions take different times depending on the length of the next instruction executed. On the 8088 and 8086, m is never a factor. On the 80286, m is the number of bytes in the instruction. On the 80386/486, m is the number of components. Each byte of encoding is a component, and the displacement and data are separate components. W88,88 8088 exceptions. See "Timings on the 8088 and 8086 Processors." Clocks can be converted to nanoseconds by dividing one microsecond by the number of megahertz (MHz) at which the processor is running. For example, on a processor running at 8 MHz, one clock takes 125 nanoseconds (1000 MHz per nanosecond / 8 MHz). The clock counts are for best-case timings. Actual timings vary depending on wait states, alignment of the instruction, the status of the prefetch queue, and other factors. Timings on the 8088 and 8086 Processors Because of its 8-bit data bus, the 8088 always requires two fetches to get a 16-bit operand. Instructions that work on 16-bit memory operands therefore take longer on the 8088 than on the 8086. Separate 8088 timings are shown in parentheses following the main timing. For example, 9 (W88=13) means that the 8086 with any operands or the 8088 with byte operands take 9 clocks, but the 8088 with word operands takes 13 clocks. Similarly, 16 (88=24) means that the 8086 takes 16 clocks, but the 8088 takes 24 clocks. On the 8088 and 8086, the effective address (EA) value must be added for instructions that operate on memory operands. A displacement is any direct memory or constant operand, or any combination of the two. Below are the number of clocks to add for the effective address. ╓┌───────────────────────────────┌──────────┌────────────────────────────────╖ ──────────────────────────────────────────────────────────────────────────── Components EA Clocks Examples Displacement 6 mov ax,stuffmov ax,stuff+2 Base or index 5 mov ax,[bx]mov ax,[di] ──────────────────────────────────────────────────────────────────────────── Displacementplus base or index 9 mov ax,[bp+8]mov ax,stuff[di] Base plus index (BP+DI,BX+SI) 7 mov ax,[bx+si]mov ax,[bp+di] Base plus index (BP+SI,BX+DI) 8 mov ax,[bx+di]mov ax,[bp+si] Base plus indexplus 11 mov ax,stuff[bx+si]mov displacement (BP+DI+disp ax,[bp+di+8] ,BX+SI+disp) Base plus indexplus 12 mov ax,stuff[bx+di]mov displacement (BP+SI+disp ax,[bp+si+20] ,BX+DI+disp) Segment override EA+2 mov ax,es:stuffmov ax,ds:[bp+10] Timings on the 80286-80486 Processors On the 80286-80486 processors, the effective address calculation is handled by hardware and is therefore not a factor in clock calculations except in one case. If a memory operand includes all three possible elements--a displacement, a base register, and an index register--then add one clock. On the 80486, the extra clock is not always used. Examples are shown below. mov ax,[bx+di] ;No extra mov ax,array[bx+di] ;One extra mov ax,[bx+di+6] ;One extra Note: 80186 and 80188 timings are different from 8088, 8086, and 80286 timings. They are not shown in this manual. Timings are also not shown for protected-mode transfers through gates or for the virtual 8086 mode available on the 80386/486 processors. Interpreting Encodings Encodings are shown for each variation of the instruction. This section describes encoding for all processors except the 80386/486. The encodings take the form of boxes filled with 0s and 1s for bits that are constant for the instruction variation, and abbreviations (in italics) for the following variable bits or bitfields: d Direction bit. If set, do memory to register or register to register; the reg field is the destination. If cleared, do register to memory; the reg field is the source. w Word/byte bit. If set, use 16-bit or 32-bit operands. If cleared, use 8-bit operands. s Sign bit. If set, sign-extend 8-bit immediate data to 16 bits. mod Mode. This two-bit field gives the register/memory mode with displacement. The possible values are shown below. mod Meaning 00 This value can have two meanings: If r/m is 110, a direct memory operand is used. If r/m is not 110, the displacement is 0 and an indirect memory operand is used. The operand must be based, indexed, or based indexed. 01 An indirect memory operand is used with an 8-bit displacement. 10 An indirect memory operand is used with a 16-bit displacement. 11 A two-register instruction is used; the reg field specifies the destination and the r/m field specifies the source. reg Register. This three-bit field specifies one of the general-purpose registers: reg 16/32 biut if w=1 8-bit if w=0 000 AX/EAX AL 001 CX/ECX CL 010 DX/EDX DL 011 BX/EBX BL 100 SP/ESP AH 101 BP/EBP CH 110 SI/ESI DH 111 DI/EDI BH The reg field is sometimes used to specify encoding information rather than a register. sreg Segment register. This field specifies one of the segment registers. sreg Register 000 ES 001 CS 010 SS 011 DS 100 FS 101 GS r/m Register/memory. This three-bit field specifies a register or memory r/m operand. If the mod field is 11, r/m specifies the source register using the reg field codes. Otherwise, the field has one of the following values: r/m Operand Address 000 DS:[BX+SI+disp] 001 DS:[BX+DI+disp] 010 SS:[BP+SI+disp] 011 SS:[BP+DI+disp] 100 DS:[SI+disp] 101 DS:[DI+disp] 110 SS:[BP+disp]* * If mod is 00 and r/m is 110, then the operand is treated as a direct memory operand. This means that the operand [BP] is encoded as [BP+0] rather than having a short-form like other register indirect operands. Encoding [BX] takes one byte, but encoding [BP] takes two. 111 DS:[BX+disp] disp Displacement. These bytes give the offset for memory operands. The possible lengths (in bytes) are shown in parentheses. data Data. These bytes gives the actual value for constant values. The possible lengths (in bytes) are shown in parentheses. If a memory operand has a segment override, the entire instruction has one of the following bytes as a prefix: Prefix Segment 00101110 (2Eh) CS 00111110 (3Eh) DS 00100110 (26h) ES 00110110 (36h) SS 01100100 (64h) FS 01100101 (65h) GS Example As an example, assume you want to calculate the encoding for the following statement (where warray is a 16-bit variable): add warray[bx+di],-3 First look up the encoding for the immediate to memory syntax of the ADD instruction: 100000sw mod,000,r/m data (0, 1, or 2) Since the destination is a word operand, the w bit is set. The 8-bit immediate data must be sign-extended to 16 bits in order to fit into the operand, so the s bit is also set. The first byte of the instruction is therefore 10000011 (83h). Since the memory operand can be anywhere in the segment, it must have a 16-bit offset (displacement). Therefore the mod field is 10. The reg field is 000, as shown in the encoding. The r/m coding for [bx+di+disp] is 001. The second byte is 10000001 (81h). The next two bytes are the offset of warray. The low byte of the offset is stored first and the high byte second. For this example, assume that warray is located at offset 10EFh. The last byte of the instruction is used to store the 8-bit immediate value -3 (FDh). This value is encoded as 8 bits (but sign-extended to 16 bits by the processor). 83 81 EF 10 FD You can confirm this by assembling the instruction and looking at the resulting assembly listing. Interpreting 80386/486 Encoding Extensions This book shows 80386/486 encodings for instructions that are available only on the 80386/486 processors. For other instructions, encodings are shown only for the 16-bit subset available on all processors. This section tells how to convert the 80286 encodings shown in the book to 80386/486 encodings that use extensions such as 32-bit registers and memory operands. The extended 80386/486 encodings differ in that they can have additional prefix bytes, a Scaled Index Base (SIB) byte, and 32-bit displacement and immediate bytes. Use of these elements is closely tied to the segment word size. The use type of the code segment determines whether the instructions are processed in 32-bit mode (USE32) or 16-bit mode (USE16). Current versions of MS-DOS(R) and Microsoft Windows and version 1.x of OS/2 use 16-bit mode only. Version 2.0 of OS/2 uses 32-bit mode. Additional bytes may be added for a segment prefix, a repeat prefix, or the LOCK prefix. Address-Size Prefix The address-size prefix determines the segment word size of the operation. It can override the default size for calculating the displacement of memory addresses. The address prefix byte is 67h. The assembler automatically inserts this byte where appropriate. In 32-bit mode (USE32 or FLAT code segment), displacements are calculated as 32-bit addresses. The effective address-size prefix must be used for any instructions that must calculate addresses as 16-bit displacements. In 16-bit mode the defaults are reversed. The prefix must be used to specify calculation of 32-bit displacements. Operand-Size Prefix The operand-size prefix determines the size of operands. It can override the default size of registers or memory operands. The operand-size prefix byte is 66h. The assembler automatically inserts this byte where appropriate. In 32-bit mode, the default sizes for operands are 8 bits and 32 bits (depending on the w bit). For most instructions, the operand-size prefix must be used for any instructions that use 16-bit operands. In 16-bit mode, the default sizes are 8 bits and 16 bits. The prefix must be used for any instructions that use 32-bit operands. Some instructions use 16-bit operands, regardless of mode. Encoding Differences for 32-Bit Operations When 32-bit operations are performed, the meaning of certain bits or fields are different than for 16-bit operations. The changes may affect default operations in 32-bit mode, or 16-bit mode operations in which the address-size prefix or the operand-size prefix is used. The following fields may have a different meaning for 32-bit operations than the meaning described in the "Interpreting Encodings" section: w Word/byte bit. If set, use 32-bit operands. If cleared, use 8-bit operands. s Sign bit. If set, sign-extend 8-bit or 16-bit immediate data to 32 bits. mod Mode. This field indicates the register/memory mode. The value 11 still indicates a register-to-register operation with r/m containing the code for a 32-bit source register. However, other codes have different meanings as shown in the tables in the next section. reg Register. The codes for 16-bit registers are extended to 32-bit registers. For example, if the reg field is 000, EAX is used instead of AX. Use of 8-bit registers is unchanged. sreg Segment register. The 80386 has the following additional segment registers: sreg Register 100 FS 101 GS r/m Register/memory. If the r/m field is used for the source register, 32-bit registers are used as for the reg field. If the field is used for memory operands, the meaning is completely different than for 16-bit operations, as shown in the tables in the next section. disp Displacement. This field is four bytes for 32-bit addresses. data Data. Immediate data can be up to four bytes. Scaled Index Base Byte Many 80386/486 extended memory operands are too complex to be represented by a single mod-reg-r/m byte. For these operands, a value of 100 in the r/m field signals the presence of a second encoding byte called the Scaled Index Base (SIB) byte. The SIB byte is made up of the following fields: ss Scaling Field. This two-bit field specifies one of the following scaling factors: ss Scale 00 1 01 2 10 4 11 8 index Index Register. This three-bit field specifies one of the following index registers: index Register 000 EAX 001 ECX 010 EDX 011 EBX 100 no index 101 EBP 110 ESI 111 EDI Note that ESP cannot be an index register. If the index field is 100, then the ss field must be 00. base Base Register. This three-bit field combines with the mod field to specify the base register and the displacement. Note that the base field only specifies the base when the r/m field is 100. Otherwise, the r/m field specifies the base. If a memory operand has a segment override, the entire instruction has one of the prefixes discussed earlier in the "Interpreting Encodings" section or one of the following prefixes for the segment registers available only on the 80386/486: Prefix Segment 01100100 (64h) FS 01100101 (65h) GS Example Assume you want to calculate the encoding for the following statement (where warray is a 16-bit variable). Assume also that the instruction is used in 16-bit mode. add warray[eax+ecx*2],-3 First look up the encoding for the immediate to memory syntax of the ADD instruction: 100000sw mod,000,r/m This encoding must be expanded to account for 80386/486 extensions. Note that the instruction operates on 16-bit data in a 16-bit mode program. Therefore, the operand-size prefix is not needed. However, the instruction does use 32-bit registers to calculate a 32-bit effective address. Thus the first byte of the encoding must be the effective address-size prefix, 01100111 (67h). The opcode byte is the same (83h) as for the 80286 example described in the "Interpreting Encodings" section. The mod-reg-r/m byte must specify a based indexed operand with a scaling factor of two. This operand cannot be specified with a single byte, so the encoding must also use the SIB byte. The value 100 in the r/m field specifies an SIB byte. The reg field is 000, as shown in the encoding. The mod field is 10 for operands that have base and scaled index registers and a 32-bit displacement. The combined mod, reg, and r/m fields for the second byte are 10000100 (84h). The SIB byte is next. The scaling factor is 2, so the ss field is 01. The index register is ECX, so the index field is 001. The base register is EAX, so the base field is 000. The SIB byte is 01001000 (48h). The next four bytes are the offset of warray. The low bytes are stored first. For this example, assume that warray is located at offset 10EFh. This offset only requires two bytes, but four must be supplied because of the addressing mode. A 32-bit address can be safely used in 16-bit mode as long as the upper word is 0. The last byte of the instruction is used to store the 8-bit immediate value -3 (FDh). The encoding is shown below in hexadecimal: 67 83 84 48 00 00 EF 10 FD Processor Instructions AAA ASCII Adjust after Addition Adjusts the result of an addition to a decimal digit (0-9). The previous addition instruction should place its 8-bit sum in AL. If the sum is greater than 9h, AH is incremented and the carry and auxiliary carry flags are set. Otherwise, the carry and auxiliary carry flags are cleared. AAD ASCII Adjust before Division Converts unpacked BCD digits in AH (most significant digit) and AL (least significant digit) to a binary number in AX. This instruction is often used to prepare an unpacked BCD number in AX for division by an unpacked BCD digit in an 8-bit register. AAM ASCII Adjust after Multiply Converts an 8-bit binary number less than 100 decimal in AL to an unpacked BCD number in AX. The most significant digit goes in AH and the least significant in AL. This instruction is often used to adjust the product after a MUL instruction that multiplies unpacked BCD digits in AH and AL. It is also used to adjust the quotient after a DIV instruction that divides a binary number less than 100 decimal in AX by an unpacked BCD number. AAS ASCII Adjust after Subtraction Adjusts the result of a subtraction to a decimal digit (0-9). The previous subtraction instruction should place its 8-bit result in AL. If the result is greater than 9h, AH is decremented and the carry and auxiliary carry flags are set. Otherwise, the carry and auxiliary carry flags are cleared. ADC Add with Carry Adds the source operand, the destination operand, and the value of the carry flag. The result is assigned to the destination operand. This instruction is used to add the more significant portions of numbers that must be added in multiple registers. ADD Add Adds the source and destination operands and puts the sum in the destination operand. AND Logical AND Performs a bitwise AND operation on the source and destination operands and stores the result in the destination operand. For each bit position in the operands, if both bits are set, the corresponding bit of the result is set. Otherwise, the corresponding bit of the result is cleared. ARPL Adjust Requested Privilege Level 80286-80486 Protected Only Verifies that the destination Requested Privilege Level (RPL) field (bits 0 and 1 of a selector value) is less than the source RPL field. If it is not, ARPL adjusts the destination RPL up to match the source RPL. The destination operand should be a 16-bit memory or register operand containing the value of a selector. The source operand should be a 16-bit register containing the test value. The zero flag is set if the destination is adjusted; otherwise, the flag is cleared. ARPL is useful only in 80286-80486 protected mode. See Intel documentation for details on selectors and privilege levels. BOUND Check Array Bounds 80186-80486 Only Verifies that a signed index value is within the bounds of an array. The destination operand can be any 16-bit register containing the index to be checked. The source operand must then be a 32-bit memory operand in which the low and high words contain the starting and ending values, respectively, of the array. (On the 80386/486 processors, the destination operand can be a 32-bit register; in this case, the source operand must be a 64-bit operand made up of 32-bit bounds.) If the source operand is less than the first bound or greater than the last bound, an interrupt 5 is generated. The instruction pointer pushed by the interrupt (and returned by IRET) points to the BOUND instruction rather than to the next instruction. BSF/BSR Bit Scan 80386/486 Only Scans an operand to find the first set bit. If a set bit is found, the zero flag is set and the destination operand is loaded with the bit index of the first set bit encountered. If no set bit is found, the zero flag is cleared. BSF (Bit Scan Forward) scans from bit 0 to the most significant bit. BSR (Bit Scan Reverse) scans from the most significant bit of an operand to bit 0. BSWAP Byte Swap 80486 Only Takes a single 32-bit register as operand and exchanges the first byte with the fourth and the second byte with the third. This instruction does not alter any bit values within the bytes and is useful for quickly translating between 8086-family byte storage and storage schemes in which the high byte is stored first. BT/BTC/BTR/BTS Bit Tests 80386/486 Only Copies the value of a specified bit into the carry flag, where it can be tested by a JC or JNC instruction. The destination operand specifies the value in which the bit is located; the source operand specifies the bit position. BT simply copies the bit to the flag. BTC copies the bit and complements (toggles) it in the destination. BTR copies the bit and resets (clears) it in the destination. BTS copies the bit and sets it in the destination. CALL Call Procedure Calls a procedure. The instruction pushes the address of the next instruction onto the stack and jumps to the address specified by the operand. For NEAR calls, SP is decreased by 2, the offset (IP) is pushed, and the new offset is loaded into IP. For FAR calls, SP is decreased by 2, the segment (CS) is pushed, and the new segment is loaded into CS. Then SP is decreased by 2 again, the offset (IP) is pushed, and the new offset is loaded into IP. A subsequent RET instruction can pop the address so that execution continues with the instruction following the call. CBW Convert Byte to Word Converts a signed byte in AL to a signed word in AX by extending the sign bit of AL into all bits of AH. CDQ Convert Double to Quad 80386/486 Only Converts the signed doubleword in EAX to a signed quadword in the EDX:EAX register pair by extending the sign bit of EAX into all bits of EDX. CLC Clear Carry Flag Clears the carry flag. CLD Clear Direction Flag Clears the direction flag. All subsequent string instructions will process up (from low addresses to high addresses) by increasing the appropriate index registers. CLI Clear Interrupt Flag Clears the interrupt flag. When the interrupt flag is cleared, maskable interrupts are not recognized until the flag is set again with the STI instruction. In protected mode, CLI only clears the flag if the current task's privilege level is less than or equal to the value of the IOPL flag. Otherwise, a general-protection fault occurs. CLTS Clear Task Switched Flag 80286-80486 Privileged Only Clears the task switched flag in the Machine Status Word (MSW) of the 80286 or the CR0 register of the 80386/486. This instruction can be used only in systems software executing at privilege level 0. See Intel documentation for details on the task-switched flag and other privileged-mode concepts. CMC Complement Carry Flag Complements (toggles) the carry flag. CMP Compare Two Operands Compares two operands as a test for a subsequent conditional-jump or set instruction. CMP does this by subtracting the source operand from the destination operand and setting the flags according to the result. CMP is the same as the SUB instruction, except that the result is not stored. CMPS/CMPSB/ CMPSW/CMPSD Compare String Compares two strings. DS:SI must point to the source string and ES:DI must point to the destination string (even if operands are given). For each comparison, the destination element is subtracted from the source element and the flags are updated to reflect the result (although the result is not stored). DI and SI are adjusted according to the size of the operands and the status of the direction flag. They are increased if the direction flag has been cleared with CLD or decreased if the direction flag has been set with STD. If the CMPS form of the instruction is used, operands must be provided to indicate the size of the data elements to be processed. A segment override can be given for the source (but not for the destination). If CMPSB (bytes), CMPSW (words), or CMPSD (doublewords on the 80386/486 only) is used, the instruction determines the size of the data elements to be processed. CMPS and its variations are normally used with repeat prefixes. REPNE (or REPNZ) is used to find the first match between two strings. REPE (or REPZ) is used to find the first nonmatch. Before the comparison, CX should contain the maximum number of elements to compare. After a REPNE CMPS, the zero flag will be cleared if no match was found. After a REPE CMPS, the zero flag will be set if no nonmatch was found. Otherwise, SI and DI will point to the element after the first match or nonmatch. CMPXCHG Compare and Exchange 80486 Only Compares the destination operand to the accumulator (AL, AX, or EAX). If equal, the source operand is copied to the destination. Otherwise, the destination is copied to the accumulator. The instruction sets flags according to the result of the comparison. CWD Convert Word to Double Converts the signed word in AX to a signed doubleword in the DX:AX register pair by extending the sign bit of AX into all bits of DX. CWDE Convert Word to Extended Double 80386/486 Only Converts a signed word in AX to a signed doubleword in EAX by extending the sign bit of AX into all bits of EAX. DAA Decimal Adjust after Addition Adjusts the result of an addition to a packed BCD number (less than 100 decimal). The previous addition instruction should place its 8-bit binary sum in AL. DAA converts this binary sum to packed BCD format with the least significant decimal digit in the lower four bits and the most significant digit in the upper four bits. If the sum is greater than 99h after adjustment, the carry and auxiliary carry flags are set. Otherwise, the carry and auxiliary carry flags are cleared. DAS Decimal Adjust after Subtraction Adjusts the result of a subtraction to a packed BCD number (less than 100 decimal). The previous subtraction instruction should place its 8-bit binary result in AL. DAS converts this binary sum to packed BCD format with the least significant decimal digit in the lower four bits and the most significant digit in the upper four bits. If the sum is greater than 99h after adjustment, the carry and auxiliary carry flags are set. Otherwise, the carry and auxiliary carry flags are cleared. DEC Decrement Subtracts 1 from the destination operand. Because the operand is treated as an unsigned integer, the DEC instruction does not affect the carry flag. To detect any effects on the carry flag, use the SUB instruction. DIV Unsigned Divide Divides an implied destination operand by a specified source operand. Both operands are treated as unsigned numbers. If the source (divisor) is 16 bits wide, the implied destination (dividend) is the DX:AX register pair. The quotient goes into AX and the remainder into DX. If the source is 8 bits wide, the implied destination operand is AX. The quotient goes into AL and the remainder into AH. On the 80386/486, if the source is EAX, the quotient goes into EAX and the divisor into EDX. ENTER Make Stack Frame 80186-80486 Only Creates a stack frame for a procedure that receives parameters passed on the stack. When immed16 is 0, ENTER is equivalent to push bp, followed by mov bp,sp. The first operand of the ENTER instruction specifies the number of bytes to reserve for local variables. The second operand specifies the nesting level for the procedure. The nesting level should be 0 for languages that do not allow access to local variables of higher-level procedures (such as C, Basic, and FORTRAN). See the complementary instruction LEAVE for a method of exiting from a procedure. HLT@EH@% Halt Stops CPU execution until an interrupt restarts execution at the instruction following HLT. In protected mode, this instruction works only in privileged mode. IDIV Signed Divide Divides an implied destination operand by a specified source operand. Both operands are treated as signed numbers. If the source (divisor) is 16 bits wide, the implied destination (dividend) is the DX:AX register pair. The quotient goes into AX and the remainder into DX. If the source is 8 bits wide, the implied destination is AX. The quotient goes into AL and the remainder into AH. On the 80386/486, if the source is EAX, the quotient goes into EAX and the divisor into EDX. IMUL Signed Multiply Multiplies an implied destination operand by a specified source operand. Both operands are treated as signed numbers. If a single 16-bit operand is given, the implied destination is AX and the product goes into the DX:AX register pair. If a single 8-bit operand is given, the implied destination is AL and the product goes into AX. On the 80386/486, if the operand is EAX, the product goes into the EDX:EAX register pair. The carry and overflow flags are set if the product is sign-extended into DX for 16-bit operands, into AH for 8-bit operands, or into EDX for 32-bit operands. Two additional syntaxes are available on the 80186-80486 processors. In the two-operand form, a 16-bit register gives one of the factors and serves as the destination for the result; a source constant specifies the other factor. In the three-operand form, the first operand is a 16-bit register where the result will be stored, the second is a 16-bit register or memory operand containing one of the factors, and the third is a constant representing the other factor. With both variations, the overflow and carry flags are set if the result is too large to fit into the 16-bit destination register. Since the low 16 bits of the product are the same for both signed and unsigned multiplication, these syntaxes can be used for either signed or unsigned numbers. On the 80386/486, the operands can be either 16 or 32 bits wide. A fourth syntax is available on the 80386/486. Both the source and destination operands can be given specifically. The source can be any 16- or 32-bit memory operand or general-purpose register. The destination can be any general-purpose register of the same size. The overflow and carry flags are set if the product does not fit in the destination. IN Input from Port Transfers a byte or word (or doubleword on the 80386/486) from a port to the accumulator register. The port address is specified by the source operand, which can be DX or an 8-bit constant. Constants can only be used for port numbers less than 255; use DX for higher port numbers. In protected mode, a general-protection fault occurs if IN is used when the current privilege level is greater than the value of the IOPL flag. INC Increment Adds 1 to the destination operand. Because the operand is treated as an unsigned integer, the INC instruction does not affect the carry flag. If a signed carry requires detection, use the ADD instruction. INS/INSB/INSW/INSD Input from Port to String 80186-80486 Only Receives a string from a port. The string is considered the destination and must be pointed to by ES:DI (even if an operand is given). The input port is specified in DX. For each element received, DI is adjusted according to the size of the operand and the status of the direction flag. DI is increased if the direction flag has been cleared with CLD or decreased if the direction flag has been set with STD. If the INS form of the instruction is used, a destination operand must be provided to indicate the size of the data elements to be processed and DX must be specified as the source operand containing the port number. A segment override is not allowed. If INSB (bytes), INSW (words), or INSD (doublewords on the 80386/486 only) is used, the instruction determines the size of the data elements to be received. INS and its variations are normally used with the REP prefix. Before the repeated instruction is executed, CX should contain the number of elements to be received. In protected mode, a general-protection fault occurs if INS is used when the current privilege level is greater than the value of the IOPL flag. INT Interrupt Generates a software interrupt. An 8-bit constant operand (0 to 255) specifies the interrupt procedure to be called. The call is made by indexing the interrupt number into the Interrupt Descriptor Table (IDT) starting at segment 0, offset 0. In real mode, the IDT contains 4-byte pointers to interrupt procedures. In privileged mode, the IDT contains 8-byte pointers. When an interrupt is called in real mode, the flags, CS, and IP are pushed onto the stack (in that order) and the trap and interrupt flags are cleared. STI can be used to restore interrupts. See Intel documentation and the documentation for your operating system for details on using and defining interrupts in privileged mode. To return from an interrupt, use the IRET instruction. INTO Interrupt on Overflow Generates interrupt 4 if the overflow flag is set. The default DOS behavior for interrupt 4 is to return without taking any action. You must define an interrupt procedure for interrupt 4 in order for INTO to have any effect. INVD Invalidate Data Cache 80486 Only Empties contents of the current data cache without writing changes to memory. Proper use of this instruction requires knowledge of how contents are placed in the cache. INVD is intended primarily for systems programming. See Intel documentation for details. INVLPG Invalidate TLB Entry 80486 Only Invalidates an entry in the Translation Lookaside Buffer (TLB), used by the demand-paging mechanism for OS/2 and other virtual-memory systems. The instruction takes a single memory operand and calculates the effective address of the operand, including the segment address. If the resulting address is mapped by any entry in the TLB, this entry is removed. Proper use of INVLPG requires understanding the hardware-supported demand-paging mechanism. INVLPG is intended primarily for systems programming. See Intel documentation for details. IRET/IRETD Interrupt Return Returns control from an interrupt procedure to the interrupted code. In real mode, the IRET instruction pops IP, CS, and the flags (in that order) and resumes execution. See Intel documentation for details on IRET operation in privileged mode. On the 80386/486, the IRETD instruction should be used to pop a 32-bit instruction pointer when returning from an interrupt called from a 32-bit segment. The F suffix prevents epilogue code from being generated when ending a PROC block. Use it to terminate interrupt service procedures. Jcondition Jump Conditionally Transfers execution to the specified label if the flags condition is true. The condition is tested by checking the flags shown in the table on the following page. If the condition is false, no jump is taken and program execution continues at the next instruction. On the 8086-80286 processors, the label given as the operand must be short (between -128 and +127 bytes from the instruction following the jump).* The 80386/486 processors allow near jumps (-32,768 to +32,767 bytes). On the 80386/486, the assembler generates the shortest jump possible, unless the jump size is explicitly specified. When the 80386/486 processors are in FLAT memory model, short jumps range from -128 to +127 bytes and near jumps range from -2 to +2 gigabytes. There are no far jumps. JMP Jump Unconditionally Transfers program execution to the address specified by the destination operand. Jumps are near (between -32,768 and +32,767 bytes from the instruction following the jump), or short (between -128 and +127 bytes), or far (in a different code segment). Unless a distance is explicitly specified, the assembler selects the shortest possible jump. With near and short jumps, the operand specifies a new IP address. With far jumps, the operand specifies new IP and CS addresses. When the 80386/486 processors are in FLAT memory model, short jumps range from -128 to +127 bytes and near jumps range from -2 to +2 gigabytes. LAHF Load Flags into AH Register Transfers bits 0 to 7 of the flags register to AH. This includes the carry, parity, auxiliary carry, zero, and sign flags, but not the trap, interrupt, direction, or overflow flags. LAR Load Access Rights 80286-80486 Protected Only Loads the access rights of a selector into a specified register. The source operand must be a register or memory operand containing a selector. The destination operand must be a register that will receive the access rights if the selector is valid and visible at the current privilege level. The zero flag is set if the access rights are transferred, or cleared if they are not. See Intel documentation for details on selectors, access rights, and other privileged-mode concepts. LDS/LES/LFS/LGS/LSS Load Far Pointer Reads and stores the far pointer specified by the source memory operand. The instruction moves the pointer's segment value into DS, ES, FS, GS, or SS (depending on the instruction). Then it moves the pointer's offset value into the destination operand. The LDS and LES instructions are available on all processors. The LFS, LGS, and LSS instructions are available only on the 80386/486. LEA Load Effective Address Calculates the effective address (offset) of the source memory operand and stores the result in the destination register. If the source operand is a direct memory address, the assembler encodes the instruction in the more efficient MOV reg,immediate form (equivalent to MOV reg, OFFSET mem). LEAVE High Level Procedure Exit 80186-80486 Only Terminates the stack frame of a procedure. LEAVE reverses the action of a previous ENTER instruction by restoring SP and BP to the values they had before the procedure stack frame was initialized. LEAVE is equivalent to mov sp,bp, followed by pop bp. LES/LFS/LGS Load Far Pointer to Extra Segment See LDS. LGDT/LIDT/LLDT Load Descriptor Table 80286-80486 Privileged Only Loads a value from an operand into a descriptor table register. LGDT loads into the Global Descriptor Table, LIDT into the Interrupt Descriptor Table, and LLDT into the Local Descriptor Table. These instructions are available only in privileged mode. See Intel documentation for details on descriptor tables and other protected-mode concepts. LMSW Load Machine Status Word 80286-80486 Privileged Only Loads a value from a memory operand into the Machine Status Word (MSW). This instruction is available only in privileged mode. See Intel documentation for details on the MSW and other protected-mode concepts. LOCK Lock the Bus Locks out other processors during execution of the next instruction. This instruction is a prefix. It must precede an instruction that accesses a memory location that another processor might attempt to access at the same time. See Intel documentation for details on multiprocessor environments. LODS/LODSB/ LODSW/LODSD Load String Operand Loads a string from memory into the accumulator register. The string to be loaded is the source and must be pointed to by DS:SI (even if an operand is given). For each source element loaded, SI is adjusted according to the size of the operands and the status of the direction flag. SI is increased if the direction flag has been cleared with CLD or decreased if the direction flag has been set with STD. If the LODS form of the instruction is used, an operand must be provided to indicate the size of the data elements to be processed. A segment override can be given. If LODSB (bytes), LODSW (words), or LODSD (doublewords on the 80386/486 only) is used, the instruction determines the size of the data elements to be processed and whether the element will be loaded to AL, AX, or EAX. LODS and its variations are not normally used with repeat prefixes, since there is no reason to repeatedly load memory values to a register. LOOP/LOOPW/LOOPD Loop Loops repeatedly to a specified label. LOOP decrements CX (without changing any flags) and, if the result is not 0, transfers execution to the address specified by the operand. On the 80386/486, LOOP uses the 16-bit CX in 16-bit mode and the 32-bit ECX in 32-bit mode. The default can be overridden with LOOPW (CX) or LOOPD (ECX). If CX is 0 after being decremented, execution continues at the next instruction. The operand must specify a short label (between -128 and +127 bytes from the instruction following the LOOP instruction). LOOPcondition LOOPconditionW LOOPcondition Loop Conditionally Loops repeatedly to a specified label if condition is met and if CX is not 0. On the 80386/486, these instructions use the 16-bit CX in 16-bit mode and the 32-bit ECX in 32-bit mode. This default can be overridden with the W (CX) or D (ECX) forms of the instruction. The instruction decrements CX (without changing any flags) and tests whether the zero flag was set by a previous instruction (such as CMP). With LOOPE and LOOPZ (they are synonyms), execution is transferred to the label if the zero flag is set and CX is not 0. With LOOPNE and LOOPNZ (they are synonyms), execution is transferred to the label if the zero flag is cleared and CX is not 0. Execution continues at the next instruction if the condition is not met. Before entering the loop, CX should be set to the maximum number of repetitions desired. LSL Load Segment Limit 80286-80486 Protected Only Loads the segment limit of a selector into a specified register. The source operand must be a register or memory operand containing a selector. The destination operand must be a register that will receive the segment limit if the selector is valid and visible at the current privilege level. The zero flag is set if the segment limit is transferred, or cleared if it is not. See Intel documentation for details on selectors, segment limits, and other protected-mode concepts. LSS Load Far Pointer to Stack Segment See LDS. LTR Load Task Register 80286-80486 Privileged Only Loads a value from the specified operand to the current task register. LTR is available only in privileged mode. See Intel documentation for details on task registers and other protected-mode concepts. MOV Move Data Moves the value in the source operand to the destination operand. If the destination operand is SS, interrupts are disabled until the next instruction is executed (except on early versions of the 8088 and 8086). MOV Move to/from Special Registers 80386/486 Only Moves a value from a special register to or from a 32-bit general-purpose register. The special registers include the control registers CR0, CR2, and CR3; the debug registers DR0, DR1, DR2, DR3, DR6, and DR7; and the test registers TR6 and TR7. On the 80486, the test registers TR4, TR5, and TR7 are also available. See Intel documentation for details on special registers. MOVS/MOVSB/ MOVSW/MOVSD Move String Data Moves a string from one area of memory to another. The source string must be pointed to by DS:SI, and the destination address must be pointed to by ES:DI (even if operands are given). For each element moved, DI and SI are adjusted according to the size of the operands and the status of the direction flag. They are increased if the direction flag has been cleared with CLD, or decreased if the direction flag has been set with STD. If the MOVS form of the instruction is used, operands must be provided to indicate the size of the data elements to be processed. A segment override can be given for the source operand (but not for the destination). If MOVSB (bytes), MOVSW (words), or MOVSD (doublewords on the 80386/486 only) is used, the instruction determines the size of the data elements to be processed. MOVS and its variations are normally used with the REP prefix. MOVSX Move with Sign-Extend 80386/486 Only Moves and sign-extends the value of the source operand to the destination register. MOVSX is used to copy a signed 8-bit or 16-bit source operand to a larger 16-bit or 32-bit destination register. MOVZX Move with Zero-Extend 80386/486 Only Moves and zero-extends the value of the source operand to the destination register. MOVZX is used to copy an unsigned 8-bit or 16-bit source operand to a larger 16-bit or 32-bit destination register. MUL Unsigned Multiply Multiplies an implied destination operand by a specified source operand. Both operands are treated as unsigned numbers. If a single 16-bit operand is given, the implied destination is AX and the product goes into the DX:AX register pair. If a single 8-bit operand is given, the implied destination is AL and the product goes into AX. On the 80386/486, if the operand is EAX, the product goes into the EDX:EAX register pair. The carry and overflow flags are set if DX is not 0 for 16-bit operands or if AH is not 0 for 8-bit operands. NEG Two's Complement Negation Replaces the operand with its two's complement. NEG does this by subtracting the operand from 0. If the operand is 0, the carry flag is cleared. Otherwise, the carry flag is set. If the operand contains the maximum possible negative value (-128 for 8-bit operands or -32,768 for 16-bit operands), the value does not change, but the overflow and carry flags are set. NOP No Operation Performs no operation. NOP can be used for timing delays or alignment. NOT One's Complement Negation Toggles each bit of the operand by clearing set bits and setting cleared bits. OR Inclusive OR Performs a bitwise OR operation on the source and destination operands and stores the result to the destination operand. For each bit position in the operands, if either or both bits are set, the corresponding bit of the result it set. Otherwise, the corresponding bit of the result is cleared. OUT Output to Port Transfers a byte or word (or a doubleword on the 80386/486) to a port from the accumulator register. The port address is specified by the destination operand, which can be DX or an 8-bit constant. In protected mode, a general-protection fault occurs if OUT is used when the current privilege level is greater than the value of the IOPL flag. OUTS/OUTSB/ OUTSW/OUTSD Output String to Port 80186-80486 Only Sends a string to a port. The string is considered the source and must be pointed to by DS:SI (even if an operand is given). The output port is specified in DX. For each element sent, SI is adjusted according to the size of the operand and the status of the direction flag. SI is increased if the direction flag has been cleared with CLD or decreased if the direction flag has been set with STD. If the OUTS form of the instruction is used, an operand must be provided to indicate the size of data elements to be sent. A segment override can be given. If OUTSB (bytes), OUTSW (words), or OUTSD (doublewords on the 80386/486 only) is used, the instruction determines the size of the data elements to be sent. OUTS and its variations are normally used with the REP prefix. Before the instruction is executed, CX should contain the number of elements to send. In protected mode, a general-protection fault occurs if OUTS is used when the current privilege level is greater than the value of the IOPL flag. POP Pop Pops the top of the stack into the destination operand. The value at SS:SP is copied to the destination operand and SP is increased by 2. The destination operand can be a memory location, a general-purpose 16-bit register, or any segment register except CS. Use RET to pop CS. On the 80386/486, 32-bit values can be popped by giving a 32-bit operand. ESP is increased by 4 for 32-bit pops. POPA/POPAD Pop All 80186-80486 Only Pops the top 16 bytes on the stack into the 8 general-purpose registers. The registers are popped in the following order: DI, SI, BP, SP, BX, DX, CX, AX. The value for the SP register is actually discarded rather than copied to SP. POPA always pops into 16-bit registers. On the 80386/486, use POPAD to pop into 32-bit registers. POPF/POPFD Pop Flags Pops the value on the top of the stack into the flags register. POPF always pops into the 16-bit flags register. On the 80386/486, use POPFD to pop into the 32-bit flags register. PUSH/PUSHW/PUSHD Push Pushes the source operand onto the stack. SP is decreased by 2 and the source value is copied to SS:SP. The operand can be a memory location, a general-purpose 16-bit register, or a segment register. On the 80186-80486 processors, the operand can also be a constant. On the 80386/486, 32-bit values can be pushed by specifying a 32-bit operand. ESP is decreased by 4 for 32-bit pushes. On the 8088 and 8086, PUSH SP saves the value of SP after the push. On the 80186-80486 processors, PUSH SP saves the value of SP before the push. The PUSHW and PUSHD instructions push a word (2 bytes) and a doubleword (4 bytes), respectively. PUSHA/PUSHAD Push All 80186-80486 Only Pushes the eight general-purpose registers onto the stack. The registers are pushed in the following order: AX, CX, DX, BX, SP, BP, SI, DI. The value pushed for SP is the value before the instruction. PUSHA always pushes 16-bit registers. On the 80386/486, use PUSHAD to push 32-bit registers. PUSHF/PUSHFD Push Flags Pushes the flags register onto the stack. PUSHF always pushes the 16-bit flags register. On the 80386/486, use PUSHFD to push the 32-bit flags register. RCL/RCR/ROL/ROR Rotate Rotates the bits in the destination operand the number of times specified in the source operand. RCL and ROL rotate the bits left; RCR and ROR rotate right. ROL and ROR rotate the number of bits in the operand. For each rotation, the leftmost or rightmost bit is copied to the carry flag as well as rotated. RCL and RCR rotate through the carry flag. The carry flag becomes an extension of the operand so that a 9-bit rotation is done for 8-bit operands, or a 17-bit rotation for 16-bit operands. On the 8088 and 8086, the source operand can be either CL or 1. On the 80186-80486, the source operand can be CL or an 8-bit constant. On the 80186-80486, rotate counts larger than 31 are masked off, but on the 8088 and 8086, larger rotate counts are performed despite the inefficiency involved. The overflow flag is only modified by single-bit variations of the instruction; for multiple-bit variations, it is undefined. REP Repeat String Repeats a string instruction the number of times indicated by CX. First, CX is compared to zero; if it equals zero, execution proceeds to the next instruction. Otherwise, CX is decremented, the string instruction is performed, and the loop continues with CX being compared to zero. REP is used with MOVS and STOS. REP can also be used with INS and OUTS on the 80186-80486 processors. On all processors except the 80386/486, combining a repeat prefix with a segment override can cause errors if an interrupt occurs. REPcondition Repeat String Conditionally Repeats a string instruction as long as condition is true and the maximum count has not been reached. REPE and REPZ (they are synonyms) repeat while the zero flag is set. REPNE and REPNZ (they are synonyms) repeat while the zero flag is cleared. The conditional-repeat prefixes should only be used with SCAS and CMPS, since these are the only string instructions that modify the zero flag. Before executing the instruction, CX should be set to the maximum allowable number of repetitions. First, CX is compared to zero; if it equals zero, execution proceeds to the next instruction. Otherwise, CX is decremented, the string instruction is performed, and the loop continues with CX being compared to zero. On all processors except the 80386/486, combining a repeat prefix with a segment override may cause errors if an interrupt occurs during a string operation. RET/RETN/RETF Return from Procedure Returns from a procedure by transferring control to an address popped from the top of the stack. A constant operand can be given indicating the number of additional bytes to release. The constant is normally used to adjust the stack for arguments pushed before the procedure was called. The size of a return (near or far) is the size of the procedure in which the RET is defined with the PROC directive. RETN can be used to specify a near return; RETF can specify a far return. A near return pops a word into IP. A far return pops a word into IP and then pops a word into CS. After the return, the number of bytes given in the operand (if any) is added to SP. ROL/ROR Rotate See RCL/RCR. SAHF Store AH into Flags Transfers AH into bits 0 to 7 of the flags register. This includes the carry, parity, auxiliary carry, zero, and sign flags, but not the trap, interrupt, direction, or overflow flags. SAL/SAR Shift See SHL/SHR/SAL/SAR. SBB Subtract with Borrow Adds the carry flag to the second operand, then subtracts that value from the first operand. This result is assigned to the first operand. SBB is used to subtract the least significant portions of numbers that must be processed in multiple registers. SCAS/SCASB/ SCASW/SCASD Scan String Flags Scans a string to find a value specified in the accumulator register. The string to be scanned is considered the destination and must be pointed to by ES:DI (even if an operand is specified). For each element, the destination element is subtracted from the accumulator value and the flags are updated to reflect the result (although the result is not stored). DI is adjusted according to the size of the operands and the status of the direction flag. DI is increased if the direction flag has been cleared with CLD or decreased if the direction flag has been set with STD. If the SCAS form of the instruction is used, an operand must be provided to indicate the size of the data elements to be processed. No segment override is allowed. If SCASB (bytes), SCASW (words), or SCASD (doublewords on the 80386/486 only) is used, the instruction determines the size of the data elements to be processed and whether the element scanned for is in AL, AX, or EAX. SCAS and its variations are normally used with repeat prefixes. REPNE (or REPNZ) is used to find the first match of the accumulator value. REPE (or REPZ) is used to find the first nonmatch. Before the comparison, CX should contain the maximum number of elements to compare. After a REPNE SCAS, the zero flag will be cleared if no match was found. After a REPE SCAS, the zero flag will be set if no nonmatch was found. Otherwise, ES:DI will point to the element past the first match or nonmatch. SETcondition Set Conditionally 80386/486 Only Sets the byte specified in the operand to 1 if condition is true or to 0 if condition is false. The condition is tested by checking the flags shown in the table on the following page. The instruction is used to set Boolean flags conditionally. SGDT/SIDT/SLDT Store Descriptor Table 80286-80486 Only Stores a descriptor table register into a specified operand. SGDT stores the Global Descriptor Table; SIDT, the Interrupt Descriptor Table; and SLDT, the Local Descriptor Table. These instructions are generally useful only in privileged mode. See Intel documentation for details on descriptor tables and other protected-mode concepts. SHL/SHR/SAL/SAR Shift Shifts the bits in the destination operand the number of times specified by the source operand. SAL and SHL shift the bits left; SAR and SHR shift right. With SHL, SAL, and SHR, the bit shifted off the end of the operand is copied into the carry flag and the leftmost or rightmost bit opened by the shift is set to 0. With SAR, the bit shifted off the end of the operand is copied into the carry flag and the leftmost bit opened by the shift retains its previous value (thus preserving the sign of the operand). SAL and SHL are synonyms. On the 8088 and 8086, the source operand can be either CL or 1. On the 80186-80486 processors, the source operand can be CL or an 8-bit constant. On the 80186-80486 processors, shift counts larger than 31 are masked off, but on the 8088 and 8086, larger shift counts are performed despite the inefficiency involved. The overflow flag is only modified by single-bit variations of the instruction; for multiple-bit variations, it is undefined. SHLD/SHRD Double Precision Shift 80386/486 Only Shifts the bits of the second operand into the first operand. The number of bits shifted is specified by the third operand. SHLD shifts the first operand to the left by the number of positions specified in the count. The positions opened by the shift are filled by the most significant bits of the second operand. SHRD shifts the first operand to the right by the number of positions specified in the count. The positions opened by the shift are filled by the least significant bits of the second operand. The count operand can be either CL or an 8-bit constant. If a shift count larger than 31 is given, it is adjusted by using the remainder (modulus) of a division by 32. SMSW Store Machine Status Word 80286-80486 Only Stores the Machine Status Word (MSW) into a specified memory operand. SMSW is generally useful only in protected mode. See Intel documentation for details on the MSW and other protected-mode concepts. STC Set Carry Flag Sets the carry flag. STD Set Direction Flag Sets the direction flag. All subsequent string instructions will process down (from high addresses to low addresses). STI Set Interrupt Flag Sets the interrupt flag. When the interrupt flag is set, maskable interrupts are recognized. If interrupts were disabled by a previous CLI instruction, pending interrupts will not be executed immediately; they will be executed after the instruction following STI. STOS/STOSB/ STOSW/STOSD Store String Data Stores the value in the accumulator in a string. The string to be filled is the destination and must be pointed to by ES:DI (even if an operand is given). For each source element loaded, DI is adjusted according to the size of the operands and the status of the direction flag. DI is increased if the direction flag has been cleared with CLD or decreased if the direction flag has been set with STD. If the STOS form of the instruction is used, an operand must be provided to indicate the size of the data elements to be processed. No segment override is allowed. If STOSB (bytes), STOSW (words), or STOSD (doublewords on the 80386/486 only) is used, the instruction determines the size of the data elements to be processed and whether the element comes from AL, AX, or EAX. STOS and its variations are often used with the REP prefix. Before the repeated instruction is executed, CX should contain the number of elements to store. STR Store Task Register 80286-80486 Only Stores the current task register to the specified operand. This instruction is generally useful only in privileged mode. See Intel documentation for details on task registers and other protected-mode concepts. SUB Subtract Subtracts the source operand from the destination operand and stores the result in the destination operand. TEST Logical Compare Tests specified bits of an operand and sets the flags for a subsequent conditional jump or set instruction. One of the operands contains the value to be tested. The other contains a bit mask indicating the bits to be tested. TEST works by doing a bitwise AND operation on the source and destination operands. The flags are modified according to the result, but the destination operand is not changed. This instruction is the same as the AND instruction, except the result is not stored. VERR/VERW Verify Read or Write 80286-80486 Protected Only Verifies that a specified segment selector is valid and can be read or written to at the current privilege level. VERR verifies that the selector is readable. VERW verifies that the selector can be written to. If the segment is verified, the zero flag is set. Otherwise, the zero flag is cleared. WAIT Wait Suspends processor execution until the processor receives a signal that a coprocessor has finished a simultaneous operation. It should be used to prevent a coprocessor instruction from modifying a memory location that is being modified simultaneously by a processor instruction. WAIT is the same as the coprocessor FWAIT instruction. WBINVD Write Back and Invalidate Data Cache 80486 Only Empties the contents of the current data cache but first writes changes to memory. Proper use of this instruction requires knowledge of how contents are placed in the cache. WBINVD is intended primarily for systems programming. See Intel documentation for details. XADD Exchange and Add 80486 Only Adds the source and destination operands and stores the sum in the destination; simultaneously, the original value of the destination is moved to the source. The instruction sets flags according to the result of the addition. XCHG Exchange Exchanges the values of the source and destination operands. XLAT/XLATB Translate Translates a value from one coding system to another by looking up the value to be translated in a table stored in memory. Before the instruction is executed, BX should point to a table in memory and AL should contain the unsigned position of the value to be translated from the table. After the instruction, AL contains the table value with the specified position. No operand is required, but one can be given in order to specify a segment override. DS is assumed unless a segment override is given. XLATB is a synonym for XLAT. Either version allows an operand, but neither requires one. XOR Exclusive OR Performs a bitwise exclusive OR operation on the source and destination operands and stores the result in the destination. For each bit position in the operands, if both bits are set or if both bits are cleared, the corresponding bit of the result is cleared. Otherwise, the corresponding bit of the result is set. Coprocessor Topical Cross-Reference for Coprocessor Load FLD/FILD/FBLD FXCH FLDCW FLDENV FRSTOR Store Data FST/FIST FSTP/FISTP/FBSTP FSTCW/FNSTCW FSTSW/FNSTSW FSAVE/FNSAVE FSTENV/FNSTENV Load Constant FLD1 FLDL2E FLDL2T FLDLG2 FLDLN2 FLDPI FLDZ Arithmetic FADD/FIADD FADDP FSUB/FISUB FSUBP FSUBR/FISUBR FSUBRP FMUL/FIMUL FMULP FSCALE FDIV/FIDIV FDIVP FDIVR/FIDIVR FDIVRP FABS FCHS FRNDINT FSQRT FPREM FPREM1 FXTRACT Transcendental FPTAN FPATAN FSIN FCOS FSINCOS F2XM1 FYL2X FYL2P1 FPREM FPREM1 Compare FCOM/FICOM FCOMP/FICOMP FCOMPP FUCOM FUCOMP FUCOMPP FTST FXAM FSTSW/FNSTSW Processor Control FINIT/FNINIT FFREE FNOP FWAIT FDECSTP FINCSTP FCLEX/FNCLEX FSETPM FDISI/FNDISI* FENI/FNENI* FSAVE/FNSAVE FLDCW FRSTOR FSTCW/FNSTCW FSTSW/FNSTSW FSTENV/FNSTENV Interpreting Coprocessor Instructions This section provides an alphabetical reference to instructions of the 8087, 80287, and 80387 coprocessors. The format is the same as the processor instructions except that encodings are not provided. Differences are noted below. The 80486 has the coprocessor built in. This one chip executes all the instructions listed in the previous section and this section. Syntax Syntaxes in Column 1 use the following abbreviations for operand types: reg A coprocessor stack register memreal A direct or indirect memory operand storing a real number memint A direct or indirect memory operand storing a binary integer membcd A direct or indirect memory operand storing a BCD number Examples The position of the examples in Column 2 is not related to the clock speeds in Column 3. Clock Speeds Column 3 shows the clock speeds for each processor. Sometimes an instruction may have more than one possible clock speed. The following abbreviations are used to specify variations: EA Effective address. This applies only to the 8087. See the Processor Section, "Timings on the 8088 and 8086 Processors," for an explanation of effective address timings. s,l,t Short real, long real, and 10-byte temporary real. w,d,q Word, doubleword, and quadword binary integer. to,fr To or from stack top. On the 80387 and 80486, the to clocks represent timings when ST is the destination. The fr clocks represent timings when ST is the source. Instruction Size The instruction size is always two bytes for instructions that do not access memory. For instructions that do access memory, the size is four bytes on the 8087 and 80287. On the 80387 and 80486, the size for instructions that access memory is four bytes in 16-bit mode or six bytes in 32-bit mode. On the 8087, each instruction must be preceded by the WAIT (also called FWAIT) instruction, thereby increasing the instruction's size by one byte. The assembler inserts WAIT automatically by default, or with the .8087 directive. Architecture The 8087, 80287, and 80387 coprocessors, along with the 80486, have several elements of architecture in common. All have a register stack made up of eight 80-bit data registers. These can contain floating-point numbers in the temporary real format. The coprocessors also have 14 bytes of control registers. Figure 2 shows the format of registers. The most important control registers are the control word and the status word. Figure 3 shows the format of these registers. Coprocessor Instructions F2XM1 2X-1 Calculates Y = 2X - 1. X is taken from ST. The result, Y, is returned in ST. X must be in the range 0 X 0.5 on the 8087/287, or in the range -1.0 X +1.0 on the 80387/486. FABS Absolute Value Converts the element in ST to its absolute value. FADD/FADDP/FIADD Add Adds the source to the destination and returns the sum in the destination. If two register operands are specified, one must be ST. If a memory operand is specified, the sum replaces the value in ST. Memory operands can be 32- or 64-bit real numbers or 16- or 32-bit integers. If no operand is specified, ST is added to ST(1) and the stack is popped, returning the sum in ST. For FADDP, the source must be ST; the sum is returned in the destination and ST is popped. FBLD Load BCD See FLD. FBSTP Store BCD and Pop See FST. FCHS Change Sign Reverses the sign of the value in ST. FCLEX/FNCLEX Clear Exceptions Clears all exception flags, the busy flag, and bit 7 in the status word. Bit 7 is the interrupt-request flag on the 8087 and the error-status flag on the 80287, 80387, and 80486. The instruction has wait and no-wait versions. FCOM/FCOMP/FCOMPP/ FICOM/FICOMPCompare Compares the specified source operand to ST and sets the condition codes of the status word according to the result. The instruction subtracts the source operand from ST without changing either operand. Memory operands can be 32- or 64-bit real numbers or 16- or 32-bit integers. If no operand is specified or if two pops are specified, ST is compared to ST(1) and the stack is popped. If one pop is specified with an operand, the operand is compared to ST. If one of the operands is a NAN, an invalid-operation exception occurs (see FUCOM for an alternative method of comparing on the 80387/486). FCOS Cosine 80387/486 Only Replaces a value in radians in ST with its cosine. If |ST| < 263, the C2 bit of the status word is cleared and the cosine is calculated. Otherwise, C2 is set and no calculation is performed. ST can be reduced to the required range with FPREM or FPREM1. * For operands with an absolute value greater than /4, up to 76 additional clocks may be required. For operands with an absolute value greater than /4, add n clocks where n = operand/(/4). FDECSTP Decrement Stack Pointer Decrements the stack-top pointer in the status word. No tags or registers are changed, and no data is transferred. If the stack pointer is 0, FDECSTP changes it to 7. FDISI/FNDISI Disable Interrupts 8087 Only Disables interrupts by setting the interrupt-enable mask in the control word. This instruction has wait and no-wait versions. Since the 80287, 80387, and 80486 do not have an interrupt-enable mask, the instruction is recognized but ignored on these coprocessors. FDIV/FDIVP/FIDIV Divide Divides the destination by the source and returns the quotient in the destination. If two register operands are specified, one must be ST. If a memory operand is specified, the quotient replaces the value in ST. Memory operands can be 32- or 64-bit real numbers or 16- or 32-bit integers. If no operand is specified, ST(1) is divided by ST and the stack is popped, returning the result in ST. For FDIVP, the source must be ST; the quotient is returned in the destination register and ST is popped. FDIVR/FDIVRP/FIDIVR Divide Reversed Divides the source by the destination and returns the quotient in the destination. If two register operands are specified, one must be ST. If a memory operand is specified, the quotient replaces the value in ST. Memory operands can be 32- or 64-bit real numbers or 16- or 32-bit integers. If no operand is specified, ST is divided by ST(1) and the stack is popped, returning the result in ST. For FDIVRP, the source must be ST; the quotient is returned in the destination register and ST is popped. FENI/FNENI Enable Interrupts 8087 Only Enables interrupts by clearing the interrupt-enable mask in the control word. This instruction has wait and no-wait versions. Since the 80287, 80387, and 80486 do not have an interrupt-enable mask, the instruction is recognized but ignored on these coprocessors. FFREE Free Register Changes the specified register's tag to empty without changing the contents of the register. FIADD/FISUB/FISUBR/ FIMUL/FIDIV/FIDIVR Integer Arithmetic See FADD, FSUB, FSUBR, FMUL, FDIV, and FDIVR. FICOM/FICOMP Compare Integer See FCOM. FILD Load Integer See FLD. FINCSTP Increment Stack Pointer Increments the stack-top pointer in the status word. No tags or registers are changed, and no data is transferred. If the stack pointer is 7, FINCSTP changes it to 0. FINIT/FNINIT Initialize Coprocessor Initializes the coprocessor and resets all the registers and flags to their default values. The instruction has wait and no-wait versions. On the 80387/486, the condition codes of the status word are cleared. On the 8087/287, they are unchanged. FIST/FISTP Store Integer See FST. FLD/FILD/FBLD Load Pushes the specified operand onto the stack. All memory operands are automatically converted to temporary-real numbers before being loaded. Memory operands can be 32-, 64-, or 80-bit real numbers or 16-, 32-, or 64-bit integers. FLD1/FLDZ/FLDPI/FLDL2E/ FLDL2T/FLDLG2/FLDLN2 Load Constant Pushes a constant onto the stack. FLDCW Load Control Word Loads the specified word into the coprocessor control word. The format of the control word is shown in the "Interpreting Coprocessor Instructions" section. FLDENV/FLDENVW/FLDENVD Load Environment State Loads the 14-byte coprocessor environment state from a specified memory location. The environment includes the control word, status word, tag word, instruction pointer, and operand pointer. On the 80387/486 in 32-bit mode, the environment state is 28 bytes. FMUL/FMULP/FIMUL Multiply Multiplies the source by the destination and returns the product in the destination. If two register operands are specified, one must be ST. If a memory operand is specified, the product replaces the value in ST. Memory operands can be 32- or 64-bit real numbers or 16- or 32-bit integers. If no operand is specified, ST(1) is multiplied by ST and the stack is popped, returning the product in ST. For FMULP, the source must be ST; the product is returned in the destination register and ST is popped. FNinstruction No-Wait Instructions Instructions that have no-wait versions include FCLEX, FDISI, FENI, FINIT, FSAVE, FSTCW, FSTENV, and FSTSW. Wait versions of instructions check for unmasked numeric errors; no-wait versions do not. When the .8087 directive is used, the assembler puts a WAIT instruction before the wait versions and a NOP instruction before the no-wait versions. FNOP No Operation Performs no operation. FNOP can be used for timing delays or alignment. FPATAN Partial Arctangent Finds the partial tangent by calculating Z = ARCTAN(Y / X). X is taken from ST and Y from ST(1). On the 8087/287, Y and X must be in the range 0 Y < X < . On the 80387/486, there is no restriction on X and Y. X is popped from the stack and Z replaces Y in ST. FPREM Partial Remainder Calculates the remainder of ST divided by ST(1), returning the result in ST. The remainder retains the same sign as the original dividend. The calculation uses the following formula: Condition Codes for FPREM and FPREM1 C3 C2 C1 C0 Meaning ? 1 ? ? Incomplete reduction 0 0 0 0 quotient MOD 8 = 0 0 0 0 1 quotient MOD 8 = 4 0 0 1 0 quotient MOD 8 = 1 0 0 1 1 quotient MOD 8 = 5 1 0 0 0 quotient MOD 8 = 2 1 0 0 1 quotient MOD 8 = 6 1 0 1 0 quotient MOD 8 = 3 1 0 1 1 quotient MOD 8 = 7 FPREM1 Partial Remainder (IEEE Compatible) 80387/486 Only Calculates the remainder of ST divided by ST(1), returning the result in ST. The remainder retains the same sign as the original dividend. FPTAN Partial Tangent Finds the partial tangent by calculating Y / X = TAN(Z). Z is taken from ST. Z must be in the range 0 Z / 4 on the 8087/287. On the 80387/486, |Z| must be less than 263. The result is the ratio Y / X. Y replaces Z, and X is pushed into ST. Thus, Y is returned in ST(1) and X in ST. FRNDINT Round to Integer Rounds ST from a real number to an integer. The rounding control (RC) field of the control word specifies the rounding method, as shown in the introduction to this section. FRSTOR/FRSTORW/FRSTORD Restore Saved State Restores the 94-byte coprocessor state to the coprocessor from the specified memory location. In 32-bit mode on the 80387/486, the environment state takes 108 bytes. FSAVE/FSAVEW/FSAVED FNSAVE/FNSAVEW/FNSAVED Save Coprocessor State Stores the 94-byte coprocessor state to the specified memory location. In 32-bit mode on the 80387/486, the environment state takes 108 bytes. This instruction has wait and no-wait versions. After the save, the coprocessor is initialized as if FINIT had been executed. FSCALE Scale Scales by powers of 2 by calculating the function Y = Y * 2X. X is the scaling factor taken from ST(1), and Y is the value to be scaled from ST. The scaled result replaces the value in ST. The scaling factor remains in ST(1). If the scaling factor is not an integer, it will be truncated toward zero before the scaling. FSETPM Set Protected Mode 80287 Only Sets the 80287 to protected mode. The instruction and operand pointers are in the protected-mode format after this instruction. On the 80387/486, FSETPM is recognized but interpreted as FNOP, since the 80386/486 processors handle addressing identically in real and protected mode. FSIN Sine 80387/486 Only Replaces a value in radians in ST with its sine. If |ST| < 263, the C2 bit of the status word is cleared and the sine is calculated. Otherwise, C2 is set and no calculation is performed. ST can be reduced to the required range with FPREM or FPREM1. FSINCOS Sine and Cosine 80387/486 Only Computes the sine and cosine of a radian value in ST. The sine replaces the value in ST, and then the cosine is pushed onto the stack. If |ST| < 263, the C2 bit of the status word is cleared and the sine and cosine are calculated. Otherwise, C2 is set and no calculation is performed. ST can be reduced to the required range with FPREM or FPREM1. FSQRT Square Root Replaces the value of ST with its square root. (The square root of -0 is -0.) FST/FSTP/FIST/FISTP/FBSTP Store Stores the value in ST to the specified memory location or register. Temporary-real values in registers are converted to the appropriate integer, BCD, or floating-point format as they are stored. With FSTP, FISTP, and FBSTP, the ST register value is popped off the stack. Memory operands can be 32-, 64-, or 80-bit real numbers for FSTP or 16-, 32-, or 64-bit integers for FISTP. FSTCW/FNSTCW Store Control Word Stores the control word to a specified 16-bit memory operand. This instruction has wait and no-wait versions. FSTENV/FSTENVW/FSTENVD FNSTENV/FNSTENVW/FNSTENVD Store Environment State Stores the 14-byte coprocessor environment state to a specified memory location. The environment state includes the control word, status word, tag word, instruction pointer, and operand pointer. On the 80387/486 in 32-bit mode, the environment state is 28 bytes. FSTSW/FNSTSW Store Status Word Stores the status word to a specified 16-bit memory operand. On the 80287, 80387, and 80486, the status word can also be stored to the processor's AX register. This instruction has wait and no-wait versions. FSUB/FSUBP/FISUB Subtract Subtracts the source operand from the destination operand and returns the difference in the destination operand. If two register operands are specified, one must be ST. If a memory operand is specified, the result replaces the value in ST. Memory operands can be 32- or 64-bit real numbers or 16- or 32-bit integers. If no operand is specified, ST is subtracted from ST(1) and the stack is popped, returning the difference in ST. For FSUBP, the source must be ST; the difference (destination minus source) is returned in the destination register and ST is popped. FSUBR/FSUBRP/FISUBR Subtract Reversed Subtracts the destination operand from the source operand and returns the result in the destination operand. If two register operands are specified, one must be ST. If a memory operand is specified, the result replaces the value in ST. Memory operands can be 32- or 64-bit real numbers or 16- or 32-bit integers. If no operand is specified, ST(1) is subtracted from ST and the stack is popped, returning the difference in ST. For FSUBRP, the source must be ST; the difference (source minus destination) is returned in the destination register and ST is popped. FTST Test for Zero Compares ST with +0.0 and sets the condition of the status word according to the result. Condition Codes for FTST C3 C2 C1 C0 Meaning 0 0 ? 0 ST is positive 0 0 ? 1 ST is negative 1 0 ? 0 ST is 0 1 1 ? 1 ST is not comparable (NAN or projective infinity) FUCOM/FUCOMP/FUCOMPP Unordered Compare 80387/486 Only Compares the specified source to ST and sets the condition codes of the status word according to the result. The instruction subtracts the source operand from ST without changing either operand. Memory operands are not allowed. If no operand is specified or if two pops are specified, ST is compared to ST(1). If one pop is specified with an operand, the given register is compared to ST. Condition Codes for FUCOM C3 C2 C1 C0 Meaning 0 0 ? 0 ST > source 0 0 ? 1 ST < source 1 0 ? 0 ST = source 1 1 ? 1 Unordered FWAIT Wait Suspends execution of the processor until the coprocessor is finished executing. This is an alternate mnemonic for the processor WAIT instruction. FXAM Examine Reports the contents of ST in the condition flags of the status word. Condition Codes for FXAM C3 C2 C1 C0 Meaning 0 0 0 0 + Unnormal* 0 0 0 1 + NAN 0 0 1 0 - Unnormal* 0 0 1 1 - NAN 0 1 0 0 + Normal 0 1 0 1 + Infinity 0 1 1 0 - Normal 0 1 1 1 - Infinity 1 0 0 0 + 0 1 0 0 1 Empty 1 0 1 0 - 0 1 0 1 1 Empty 1 1 0 0 + Denormal 1 1 0 1 Empty* 1 1 1 0 - Denormal 1 1 1 1 Empty* * Not used on the 80387/486. Unnormals are not supported by the 80387/486. Also, the 80387/486 use two codes instead of four to identify empty registers. FXCH Exchange Registers Exchanges the specified (destination) register and ST. If no operand is specified, ST and ST(1) are exchanged. FXTRACT Extract Exponent and Significand Extracts the exponent and significand (mantissa) fields of ST. The exponent replaces the value in ST, and then the significand is pushed onto the stack. FYL2X Y log2(X) Calculates Z = Y log2(X). X is taken from ST and Y from ST(1). The stack is popped, and the result, Z, replaces Y in ST. X must be in the range 0 < X < and Y in the range - < Y < . FYL2XP1 Y log2(X+1) Calculates Z = Y log2(X + 1). X is taken from ST and Y from ST(1). The stack is popped once, and the result, Z, replaces Y in ST. X must be in the range 0 |X| < (1 - (2 / 2)). Y must be in the range - < Y < .