Microsoft Programmer's Library 1.3/Microsoft-Programers-Library-v1.3.iso/sampcode/alde_c/misc/comm/yam/yam89.csm

Text File | 1988-07-28 | 4.5 KB | 165 lines

;YAM89.CSM (YAM8 & YAM9 combined for BDSC v1.46)
;
;>>:yam8.asm 9-30-81
;
;CRCK is a program to read any CP/M file and print
;a CYCLIC-REDUNDANCY-CHECK number based on the
;CCITT standard polynominal:
;   X^16 + X^15 + X^13 + X^7 + X^4 + X^2 + X + 1
;
;Useful for checking accuracy of file transfers.
;More accurate than a simple checksum.
;
;**************************************************
;
;    unsigned crck(buffer, bufsize, oldcrc)
;
;    At start of packet, oldcrc is set to 0
;
;    crc is accumulated by:
;        oldcrc=crck(buffer, bufsize, oldcrc);
;
;    crck for file is final value of oldcrc
;
;    A Short History of this function and crckfile() in yam7.c"
;
;    1.  First version used getc and called crck once per char.
;    this took 39.2 seconds to crck all the yam C files (12357)
;
;    2.  Then crckfile was recoded to use read() instead of getc.
;    Time: 19.1 seconds
;
;    3.  Several small changes in crckfile were unsuccessful in
;    reducing this time.
;
;    4.  crck and crckfile recoded to call crck once per sector.
;    This reduced time to 11.7 seconds, same as crck itself.
;    That is the current version.  Note that the CRC polynomial used
;    here is somewhat unusual; the only thing I know sure is that
;    the answers agree with those given by the CRCK program -hence the
;    function name.
;
    maclib bds

    function crck

    call    arghak
    push    b
bytlop:    lhld    arg1
    mov    c,m
    inx    h        ;fetch (next) byte from buffer
    shld    arg1
    lhld    arg3        ; get accumulated checksum
;
;---------------------------------------------
;An 8080 routine for generating a CYCLIC-
;REDUNDANCY-CHECK.  Character leaves that
;character in location REM.  By Fred Gutman.
;From 'EDN' magazine, June 5, 1979 issue, page 84.
;
DIVP:
    MOV    A,H
    ANI    128    ;Q-BIT MASK
    PUSH    PSW    ;SAVE STATUS
    DAD    H    ;2 X R(X)
    mov    a,c
    ADD    L
    MOV    L,A
    POP    PSW
    JZ    QB2    ;IF Q-BIT IS ZERO
    MOV    A,H
    XRI    0A0H    ;MS HALF OF GEN. POLY
    MOV    H,A
    MOV    A,L
    XRI    97H    ;LS HALF OF GEN. POLY
    MOV    L,A
QB2:
    shld    arg3    ;store in accumulator
    lhld    arg2
    dcx    h
    shld    arg2    ;count number of bytes in buffer
    mov    a,h
    ora    l
    jnz    bytlop
    lhld    arg3    ;return with accumulated crck in HL
    pop    b    ;pull up ur shorts
    RET

    endfunction
;>>:yam9.asm 9-30-81
;************************************************************************
;* CRCSUBS (Cyclic Redundancy Code Subroutines) version 1.20        *
;* 8080 Mnemonics                            *
;*                                    *
;*         This subroutine will compute and check a true 16-bit        *
;*    Cyclic Redundancy Code for a message of arbitrary length.    *
;*                                    *
;*    The  use  of this scheme will guarantee detection of all    *
;*    single and double bit errors, all  errors  with  an  odd    *
;*    number  of  error bits, all burst errors of length 16 or    *
;*    less, 99.9969% of all 17-bit error bursts, and  99.9984%    *
;*    of  all  possible  longer  error bursts.  (Ref: Computer    *
;*    Networks, Andrew S.  Tanenbaum, Prentiss-Hall, 1981)        *
;*                                    *
;*                                    *
;************************************************************************
;*                                    *
;*    From: CRCSUB12.ASM                        *
;*    Designed & coded by Paul Hansknecht, June 13, 1981        *
;*                                    *
;*                                    *
;*    Copyright (c) 1981, Carpenter Associates            *
;*                Box 451                    *
;*                Bloomfield Hills, MI 48013            *
;*                313/855-3074                *
;*                                    *
;*    This program may be freely reproduced for non-profit use.    *
;*                                    *
;************************************************************************
;
;    unsigned updcrc(char, oldcrc)
;
;    At start of packet, oldcrc is set to initial value
;        oldcrc=0;
;
;    crc is accumulated by:
;        oldcrc=updcrc(char, oldcrc);
;
;    at end of packet,
;        oldcrc=updcrc(0,updcrc(0,oldcrc));
;        send(oldcrc>>8); send(oldcrc);
;
;    on receive, the return value of updcrc is checked after the
;    last call (with the second CRC byte); 0 indicates no error detected
;

    function updcrc

    push    b        ;save stack frame
    call    ma2toh        ;get char
    mov    c,a
    call    ma3toh        ;and olde crc value
    MVI    B,8
UPDLOOP:MOV    A,C
    RLC
    MOV    C,A
    MOV    A,L
    RAL
    MOV    L,A
    MOV    A,H
    RAL
    MOV    H,A
    JNC    SKIPIT
    MOV    A,H        ; The generator is X^16 + X^12 + X^5 + 1
    XRI    10H        ; as recommended by CCITT.
    MOV    H,A        ; An alternate generator which is often
    MOV    A,L        ; used in synchronous transmission protocols
    XRI    21H        ; is X^16 + X^15 + X^2 + 1. This may be
    MOV    L,A        ; used by substituting XOR 80H for XOR 10H
SKIPIT:    DCR    B        ; and XOR 05H for XOR 21H in the adjacent code.
    JNZ    UPDLOOP
    POP    B
    RET            ; return with latest crc in hl

    endfunction