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---MACRO.DOC--- Macro Facility ----- -------- This assembler contains an easy-to-use, but very powerful macro facility. The facility subsumes the capabilities of most assemblers, including operand concatenation, indefinite repeat (often called IRP), and indefinite-repeat character (IRPC). Unlike other assemblers, this assembler integrates these functions into the main macro facility; so they can be invoked without clumsy syntax, or strange characters in the macro-call operands. Simple Macro Syntax All macros must be defined before they are used. A macro definition consists of the name of the macro, followed by the word MACRO, followed by the text of the macro, followed by #EM, which marks the end of the macro. Many assembly languages require a list of dummy operand-names to follow the word MACRO. This assembler does not: the operands are denoted in the text with the fixed names #1, #2, #3, ... up to a limit of #9, for each operand in order. If there is anything following the word MACRO, it is considered part of the macro text. Examples: ; CLEAR sets the register-operand to zero. CLEAR MACRO SUB #1,#1 #EM CLEAR AX ; generates a SUB AX,AX instruction CLEAR BX ; generates a SUB BX,BX instruction ; MOVM moves the second operand to the first operand. Both operands can be ; memory-variables. MOVM MACRO MOV AX,#2 MOV #1,AX #EM VAR1 DB ? VAR2 DB ? MOVM VAR1,VAR2 ; generates MOV AX,VAR2 followed by MOV VAR1,AX Formatting in macro definitions and calls The format of a macro definition is flexible. If the macro text consists of a single instruction, the definition can be given in a single line, as in the CLEAR macro given above. There is no particular advantage to doing this, however: the assembler prunes all unnecessary spaces, blank lines, and comments from the macro text before entering the text into the symbol table. I recommend the more spread-out format of the MOVM macro, for program readability. All special macro-operators within a macro definition begin with a pound-sign #. The letters following the pound-sign can be given in either upper-case or lower-case. Pound-sign operators are recognized even within quoted strings. If you wish the pound-sign to be treated literally, and not as the start of a special macro-operator, you must give 2 consecutive pound signs: ##. For example: FOO MACRO DB '##1' DB '#1' #em FOO abc ; produces DB '#1' followed by DB 'abc' The format of the macro call line is also flexible. A macro call consists of the name of the macro, followed by the operands to be plugged into the macro. The assembler prunes leading and trailing blanks from the operands of a macro call. The operands to a macro call are always separated by commas. Also, as in all assembler source lines, a semi-colon occurring outside of a quoted-string is the start of a comment, ignored by the assembler. If you want to include commas, blanks, or semi-colons in your operands, you must enclose your operand in single-quotes. Macro operand substitution Some macro assemblers expect the operands to macro calls to follow the same syntax as the operands to instructions. In those assemblers, the operands are parsed, and reduced to numeric values before being plugged into the macro definition text. This is called "passing by value". This assembler does not pass by value, it passes by text. The only parsing of operands done by the macro processor is to determine the start and the finish of the operand text. That text is substituted, without regard for its contents, for the "#n" that appears in the macro definition. The text is interpreted by the assembler only after a complete line is expanded and as it is assembled. If the first non-blank character after the macro name is a comma, then the first operand is null: any occurrances of #1 in the macro text will be deleted, and replaced with nothing. Likewise, any two consecutive commas with no non-blanks between them will result in the corresponding null operand. Also, out-of-range operands are null; for example, #3 is a null operand if only two operands are provided in the call. Null operands to macros are not in themselves illegal. They will produce errors only if the resulting macro expansion is illegal. The method of passing by text allows operand-text to be plugged anywhere into a macro, even within symbol names. For example: ; KF_ENTRY creates an entry in the KFUNCS table, consistsing of a pointer ; to a KF_-action-routine. It also declares the corresponding CF_-symbol, ; which is the index within the table for that entry. KF_ENTRY MACRO CF_#1 EQU ($-KFUNCS)/2+080 DW KF_#1 #EM KFUNCS: KF_ENTRY UP KF_ENTRY DOWN ; The above code is equivalent to: ; ; KFUNCS: ; DW KF_UP ; DW KF_DOWN ; ; CF_UP EQU 080 ; CF_DOWN EQU 081 Quoted-string operands As mentioned before, if you want to include blanks, commas, or semicolons in your operands, you enclose the operand in single-quotes. In the vast majority of cases in which these special characters need to be part of operands, the user wants them to be quoted in the final, assembled line also. Therefore, the quotes are passed in the operand. To override this, and strip the quotes from the string, you precede the quoted string with a pound-sign. Examples: DBW MACRO DB #1 DW #2 #EM DBW 'E', E_POINTER DBW 'W', W_POINTER ; note that if quotes were not passed, the above lines would have to be ; DBW '''E''', E_POINTER; DBW '''W''', W_POINTER GENERAL_PUSH MACRO PUSH#1 #EM GENERAL_PUSH F ; generates a PUSHF instruction GENERAL_PUSH #' AX' ; generates a PUSH AX instruction The fact that I could not come up with a more useful example than GENERAL_PUSH is strong evidence that it is much better to pass the quotes as the default action. Looping by operands in macros This macro facility contains two kinds of loops: you can loop once for each operand in a range of operands; or you can loop once for each character within an operand. The first kind of loop, the R-loop, is discussed in this section; the second kind, the C-loop, is discussed later. An R-loop is a stretch of macro-definition code that is repeated when the macro is expanded. In addition to the fixed operands #1 through #9, you can specify a variable operand, whose number changes each time through the loop. You give the variable operand one of the 4 names #W, #X, #Y, or #Z. An R-loop begins with #R, followed immediately by the letter W,X,Y, or Z naming the variable, followed by the number of the first operand to be used, followed by the number of the last operand to be used. After the #Rxnn is the text to be repeated. The R-loop ends with #ER. For example: STORE3 MACRO MOV AX,#1 #RY24 ; "repeat for Y running from 2 through 4" MOV #Y,AX #ER #EM STORE3 VAR1,VAR2,VAR3,VAR4 ; the above call produces the 4 instructions MOV AX,VAR1; MOV VAR2,AX; ; MOV VAR3,AX; MOV VAR4,AX. The #L last operator and indefinite repeats The macro facility recognizes the special operator #L, which is the last operand in a macro call. #L can appear anywhere in macro text; but its big power occurs in conjunction with R-loops, to yield an indefinite-repeat facility. A common example is as follows: you can take any macro that is designed for one operand, and easily convert it into a macro that accepts any number of operands. You do this by placing the command #RX1L, "repeat for X running from 1 through L", at the start of the macro, and the command #ER at the end just before the #EM. Finally, you replace all instances of #1 in the macro with #X. We see how this works with the CLEAR macro: CLEAR MACRO #RX1L SUB #X,#X #ER #EM CLEAR AX,BX ; genearates both SUB AX,AX and SUB BX,BX in one macro-call! It is possible for R-loops to iterate zero times. In this case, the loop-text is skipped completely. For example, CLEAR without any operands would produce no expanded text. Character-loops We have seen the R-loop; now we discuss the other kind of loop in macros, the character-loop, or C-loop. In the C-loop, the variable W,X,Y, or Z does not represent an entire operand; it represents a character within an operand. You start a C-loop with #C, followed by one of the 4 letters W,X,Y, or Z, followed by a single operand-specifier. Following the #Cxn is the text of the C-loop. The C-loop ends with #EC. The macro will loop once for every character in the operand. That single character will be substituted for each instance of the indicated variable-operand. For example: PUSHC MACRO #CW1 PUSH #WX #EC#EM PUSHC ABC ; generates the 3 instructions PUSH AX; PUSH BX; PUSH CX If the C-operand is quoted in the macro call, the quotes ARE removed from the operand before passing characters to the loop. It is not necessary to precede the quoted string with a pound-sign in this case. If you do, the pound-sign will be passed as the first character. If the C-operand is a null operand (no characters in it), the loop-text is skipped completely. The "B"-before and "A"-after operators So far, we have seen that you can specify operands in your macro in fourteen different ways: 1,2,3,4,5,6,7,8,9,W,X,Y,Z,L. We now multiply these 14 possibilities, by introducing the "A" and "B" operators. You can precede any of the 14 specifiers with "A" or "B", to get the adjacent operand after or before the specified operand. For example, BL means the operand just before the last operand; in other words, the second-to-the-last operand. AZ means the operand just after the Z operand. You can even repeat, up to a limit of 4 "B"s or 3 "A"s: BBL is the third-to-last operand; #AAA9 can be used where you would want to (but cannot) use #12. In the case of the variable operand to a C-loop, the "A" and "B" specifiers denote the characters before or after the current looping-character. An example of this is given in the next section. Multiple-increments within loops We have seen that you end an R-loop with a #ER, and you end a C-loop with a #EC. We now present another way to end these loops; a way that lets you specify a larger increment to the macro's loop-counter. You can end your loops with one of the 4 additional commands #E1, #E2, #E3, or #E4. For R-loops terminated by #ER, the variable-operand advances to the next operand when the loop is made. If you end your R-loop with #E2, the variable- operand advances 2 operands, not just one. For #E3, it advances 3 operands; for #E4, 4 operands. The #E1 command is the same as #ER. The most common usage of this feature is as follows: You will recall that we generalized the CLEAR macro with an R-loop, so that it would take an indefinite number of operands. Suppose we want to do the same thing with the DBW macro. We would like DBW to take any number of operands, and alternate DBs and DWs indefinitely on the operands. This is made possible by creating an R-loop terminated by #E2: DBW MACRO #RX1L DB #X DW #AX #E2 #EM DBW 'E',E_POINTER, 'W',W_POINTER ; two pairs on the same line! The #E2 terminator means that we are looping on a pair of operands. Note the crucial usage of the "A"-after operator to specify the second operand of the operand-pair. A special note applies to the DBW macro above: the assembler just happens to accept a DW directive with no operands (it generates no object code, and issues no error). This means that DBW will accept an odd number of operands with no error, and do the expected thing (it alternates bytes and words, ending with a byte). You could likewise genralize a macro with 3 or 4 operands, to an indefinite number of triples or quadruples; by ending the R-loop with #E3 or #E4. The operands in each group would be specified by #X, #AX, #AAX, and, for #E4, #AAAX. For C-loops terminated by #E1 through #E4, the character-pointer is advanced the specified number of characters. You use this in much the same way as for R-loops, to create loops on pairs, triplets, and quadruplets of characters. For example: PUSHC2 MACRO #CZ1 PUSH #Z#AZ #E2 #EM PUSHC2 AXBXSIDI ; generates PUSH AX; PUSH BX; PUSH SI; PUSH DI Negative R-loops We now introduce another form of R-loop, called the Q-loop-- the negative repeat-loop. This loop is the same as the R-loop, except that the operand number decrements instead of increments; and the loop exits when the number falls below the finish-number, not above it. The Q-loop is specified by #Qxnn instead of #Rxnn, and #EQ instead of #ER. You can also use the multiple-decrement forms #E1 #E2 #E3 or #E4 to terminate an Q-loop. Example: MOVN MACRO #QXL2 ; "negative-repeat X from L down to 2" MOV #BX,#X #EQ#EM MOVN AX,BX,CX,DX ; generates the three instructions: ; MOV CX,DX ; MOV BX,CX ; MOV AX,BX Note: the above functionality is already built into the MOV instruction of the assembler. The macro shows how you would implement it if you did not already have this facility. Nesting of loops in macros This macro facility allows nesting of loops within each other. Since we provide the 4 identifiers W,X,Y,Z for the loop-operands, you can nest to a level of 4 without restriction-- just use a different letter for each nesting level. You can nest even deeper, subject to the restriction that a letter W,X,Y,Z refers to the innermost containing loop that defines it. Implied closing of loops If you have a loop or loops ending when the macro ends, and if the iteration count for those loops is 1, you may omit the #ER, #EC, or #EQ. The assembler closes all open loops when it sees #EM, with no error. For example, if you omit the #ER for the loop-version of the CLEAR macro, it would make no difference-- the assembler automatically places an #ER code into the macro definition for you. Local labels in macros Some assemblers have a LOCAL pseudo-op that is used in conjunction with macros. Symbols declared LOCAL to a macro have unique (and bizarre) symbol-names substituted for them each time the macro is called. This solves the problem of duplicate label definitions when a macro is called more than once. In this assembler, the problem is solved more elegantly, by having a class of generic local labels throughout assembly, not just in macros. Recall that symbols consisting of a single letter, followed by one or more decimal digits, can be redefined. You can use such labels in your macro definitions. I have recommended that local labels outside of macros be designated L1 through L9. Within macro definitions, I suggest that you use labels M1 through M9. If you used an Ln-label within a macro, you would have to make sure that you never call the macro within the range of definition of another Ln-label with the same name. By using Mn-labels, you avoid such potential conflicts. The following example of a local label within a macro is taken from the source of the macro-processor itself: ; "JPOUND label" checks to see if AL is a pound sign. If it is, it processes ; the pound-sign term, and jumps to label. Otherwise, it drops through ; to the following code. JPOUND MACRO CMP AL,'##' ; is the scanned character a pound-sign? JNE >M1 ; skip if not CALL MDEF_POUND ; process the pound sign JMP #1 ; jump to the label provided M1: #EM ... L3: ; loop here to consume empty lines and leading blanks CALL SKIP_BLANKS ; skip over the leading blanks of a line INC SI ; advance source pointer beyond the next non-blank JPOUND L3 ; if pound-sign then process, and consume more blanks CMP AL,0A ; were the blanks terminated by a linefeed? JE L3 ; loop if yes, nothing on this line L5: ; loop here after a line is seen to have contents CMP AL,';' ; have we reached the start of a comment? JE L1 ; jump if yes, to consume the comment JPOUND >L6 ; if pound-sign then process it, and get another char ... L6: LODSB ; fetch the next definition-char from the source CMP AL,' ' ; is it blank? JA L5 ; loop if not, to process it ... Debugging macro expansions There is a tool called EXMAC which will help you troubleshoot program lines that call macros. If you are not sure about what code is being generated by your macro calls, EXMAC will tell you. See the file EXMAC.DOC for details.