Help with Checksum and conversion to Exe format

From: Andrew Kennedy (andrewkennedy2_at_LOGev1.net)
Date: 03/06/04

  • Next message: C: "Re: Cost of calling a standard library function" 
    Date: Sat, 06 Mar 2004 13:25:32 -0000

    I would like to do two things with this source.

    a. Convert it to an .exe than can be compiled by either Masm or Tasm
    since buf db 0 is hardcoded, I haven't figured out how to make
    it work

    b. Incorporate the checksum into it

    My attempts at that have not worked.
    Someone told me to do the checksum on everything but the checksum value but
    I don't know how. I think I would have to move the file pointer past the
    checksum and read from there to the EOF.

    Thanks.

    ; chkfile.asm - Modifications to do a CRC on a specified file
    ;
    ; Performs a CRC crc1.com
    ; Com file
    ;
    ; Original code by James Vahn, based on Edwin T. Floyd 's CRC-32 routine.
    ; May 15, 1994 Modifications by Andrew Kennedy
    ;
    ; Furthur improvements:
    ;
    ; encrypt filename and crc values
    ;

    cseg segment
    assume cs:cseg,ds:cseg
    org 100h ;COM format

    Begin proc far

    mov ax,03D00h ;Open for read.
    mov dx,offset filename
    int 21h
    jc error2
    mov word ptr [hndl],ax
    read:
    mov ah,03Fh
    mov bx,word ptr [hndl]
    mov dx,offset buf
    mov cx,0FEFFh ;Leave room in buffer for stack.
    sub cx,dx ;Maximum buffer size.
    int 21h
    jc error3
    or ax,ax ;End of file?
    je exit
    call UpdateCRC32 ;calculate CRC.
    loop read
    exit:
    xor word ptr [initcrc],0FFFFh ;Finish CRC calculation.
    xor word ptr [initcrc+2],0FFFFh
    mov ax,word ptr [initcrc+2]
    call bin2hex ;Print CRC to screen.
    mov ax,word ptr [initcrc]
    call bin2he
    mov ax,0FFFFh
    mov word ptr[initcrc],ax
    mov word ptr[initcrc+2],ax
    mov dx,offset CRLF ;linefeed
    mov ah,09h
    int 21h
    close:
    mov bx,word ptr [hndl]
    mov ah,3Eh ;close file.
    int 21h

    mov ax,04C00h ;Normal exit to DOS.
    int 21h

    Begin endp
    ;*****************************************************

    error proc near

    mov ah,09h
    mov dx,offset errmsg
    int 21h
    mov ax,04C01h ;Exit errorlevel 1.
    int 21h
    error endp
    ;*****************************************************

    error2 proc near

    mov ah,09h
    mov dx,offset errmsg2
    int 21h
    mov ax,04C02h ;Exit errorlevel 2.
    int 21h
    error2 endp
    ;*****************************************************

    error3 proc near

    mov ah,09h
    mov dx,offset errmsg3
    int 21h
    mov ax,04C03h ;Exit errorlevel 3.
    int 21h
    error3 endp
    ;*****************************************************

    bin2hex proc near

    ;Convert AX to HEX ASCII output

    bin2he: mov cx,4 ;4 hex digits
    mov bx,10h ;divisor
    bin2h1: xor dx,dx ;zero DX for 16 bit divide
    div bx ;leaves quotient in AX
    add dl,'0' ;convert remainder to ASCII
    cmp dl,'9'
    jna bin2h2
    add dl,'A'-'9'-1
    bin2h2: push dx ;put on stack
    loop bin2h1 ;repeat
    mov cx,4
    bin2h3: pop ax ;pop most significant digit first
    mov dl,al
    mov ah,02h
    int 21h
    loop bin2h3
    ret
    bin2hex endp
    ;*****************************************************

    UpdateCRC32 proc near

    ; UpdateCRC32 takes an initial CRC value and updates it from
    ; data in 'buf'. The updated CRC is then stored in InitCRC.

    mov si,offset buf
    mov cx,ax
    jcxz bye
    les ax,[initcrc]
    mov dx,ES
    lo2:
    xor bh,bh
    mov bl,al
    lodsb
    xor bl,al
    mov al,ah
    mov ah,dl
    mov dl,dh
    xor dh,dh
    shl bx,1
    shl bx,1
    les bx,[crc32tab+bx]
    xor ax,bx
    mov bx,ES
    xor dx,bx
    loop lo2
    mov word ptr [initcrc],ax ; Store result in InitCRC
    mov word ptr [initcrc+2],dx
    bye:
    ret
    UpdateCRC32 endp

    ;*****************************************************
    ; 32 bit reverse crc table for polynomial EDB88320h (Zmodem,PKZip)
    ; X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0

    crc32tab dd 000000000h, 077073096h, 0ee0e612ch, 0990951bah, 0076dc419h
    dd 0706af48fh, 0e963a535h, 09e6495a3h, 00edb8832h, 079dcb8a4h
    dd 0e0d5e91eh, 097d2d988h, 009b64c2bh, 07eb17cbdh, 0e7b82d07h
    dd 090bf1d91h, 01db71064h, 06ab020f2h, 0f3b97148h, 084be41deh
    dd 01adad47dh, 06ddde4ebh, 0f4d4b551h, 083d385c7h, 0136c9856h
    dd 0646ba8c0h, 0fd62f97ah, 08a65c9ech, 014015c4fh, 063066cd9h
    dd 0fa0f3d63h, 08d080df5h, 03b6e20c8h, 04c69105eh, 0d56041e4h
    dd 0a2677172h, 03c03e4d1h, 04b04d447h, 0d20d85fdh, 0a50ab56bh
    dd 035b5a8fah, 042b2986ch, 0dbbbc9d6h, 0acbcf940h, 032d86ce3h
    dd 045df5c75h, 0dcd60dcfh, 0abd13d59h, 026d930ach, 051de003ah
    dd 0c8d75180h, 0bfd06116h, 021b4f4b5h, 056b3c423h, 0cfba9599h
    dd 0b8bda50fh, 02802b89eh, 05f058808h, 0c60cd9b2h, 0b10be924h
    dd 02f6f7c87h, 058684c11h, 0c1611dabh, 0b6662d3dh, 076dc4190h
    dd 001db7106h, 098d220bch, 0efd5102ah, 071b18589h, 006b6b51fh
    dd 09fbfe4a5h, 0e8b8d433h, 07807c9a2h, 00f00f934h, 09609a88eh
    dd 0e10e9818h, 07f6a0dbbh, 0086d3d2dh, 091646c97h, 0e6635c01h
    dd 06b6b51f4h, 01c6c6162h, 0856530d8h, 0f262004eh, 06c0695edh
    dd 01b01a57bh, 08208f4c1h, 0f50fc457h, 065b0d9c6h, 012b7e950h
    dd 08bbeb8eah, 0fcb9887ch, 062dd1ddfh, 015da2d49h, 08cd37cf3h
    dd 0fbd44c65h, 04db26158h, 03ab551ceh, 0a3bc0074h, 0d4bb30e2h
    dd 04adfa541h, 03dd895d7h, 0a4d1c46dh, 0d3d6f4fbh, 04369e96ah
    dd 0346ed9fch, 0ad678846h, 0da60b8d0h, 044042d73h, 033031de5h
    dd 0aa0a4c5fh, 0dd0d7cc9h, 05005713ch, 0270241aah, 0be0b1010h
    dd 0c90c2086h, 05768b525h, 0206f85b3h, 0b966d409h, 0ce61e49fh
    dd 05edef90eh, 029d9c998h, 0b0d09822h, 0c7d7a8b4h, 059b33d17h
    dd 02eb40d81h, 0b7bd5c3bh, 0c0ba6cadh, 0edb88320h, 09abfb3b6h
    dd 003b6e20ch, 074b1d29ah, 0ead54739h, 09dd277afh, 004db2615h
    dd 073dc1683h, 0e3630b12h, 094643b84h, 00d6d6a3eh, 07a6a5aa8h
    dd 0e40ecf0bh, 09309ff9dh, 00a00ae27h, 07d079eb1h, 0f00f9344h
    dd 08708a3d2h, 01e01f268h, 06906c2feh, 0f762575dh, 0806567cbh
    dd 0196c3671h, 06e6b06e7h, 0fed41b76h, 089d32be0h, 010da7a5ah
    dd 067dd4acch, 0f9b9df6fh, 08ebeeff9h, 017b7be43h, 060b08ed5h
    dd 0d6d6a3e8h, 0a1d1937eh, 038d8c2c4h, 04fdff252h, 0d1bb67f1h
    dd 0a6bc5767h, 03fb506ddh, 048b2364bh, 0d80d2bdah, 0af0a1b4ch
    dd 036034af6h, 041047a60h, 0df60efc3h, 0a867df55h, 0316e8eefh
    dd 04669be79h, 0cb61b38ch, 0bc66831ah, 0256fd2a0h, 05268e236h
    dd 0cc0c7795h, 0bb0b4703h, 0220216b9h, 05505262fh, 0c5ba3bbeh
    dd 0b2bd0b28h, 02bb45a92h, 05cb36a04h, 0c2d7ffa7h, 0b5d0cf31h
    dd 02cd99e8bh, 05bdeae1dh, 09b64c2b0h, 0ec63f226h, 0756aa39ch
    dd 0026d930ah, 09c0906a9h, 0eb0e363fh, 072076785h, 005005713h
    dd 095bf4a82h, 0e2b87a14h, 07bb12baeh, 00cb61b38h, 092d28e9bh
    dd 0e5d5be0dh, 07cdcefb7h, 00bdbdf21h, 086d3d2d4h, 0f1d4e242h
    dd 068ddb3f8h, 01fda836eh, 081be16cdh, 0f6b9265bh, 06fb077e1h
    dd 018b74777h, 088085ae6h, 0ff0f6a70h, 066063bcah, 011010b5ch
    dd 08f659effh, 0f862ae69h, 0616bffd3h, 0166ccf45h, 0a00ae278h
    dd 0d70dd2eeh, 04e048354h, 03903b3c2h, 0a7672661h, 0d06016f7h
    dd 04969474dh, 03e6e77dbh, 0aed16a4ah, 0d9d65adch, 040df0b66h
    dd 037d83bf0h, 0a9bcae53h, 0debb9ec5h, 047b2cf7fh, 030b5ffe9h
    dd 0bdbdf21ch, 0cabac28ah, 053b39330h, 024b4a3a6h, 0bad03605h
    dd 0cdd70693h, 054de5729h, 023d967bfh, 0b3667a2eh, 0c4614ab8h
    dd 05d681b02h, 02a6f2b94h, 0b40bbe37h, 0c30c8ea1h, 05a05df1bh
    dd 02d02ef8dh

    initcrc dd 0FFFFFFFFh ;Initial CRC value

    errmsg db 'File not found- Useage: CRC FILENAME.*',0Dh,0Ah,24h
    errmsg2 db 'error 2, cannot open file.',0Dh,0Ah,24h
    errmsg3 db 'error 3, cannot read file.',0Dh,0Ah,24h
    crlf db 0Dh,0Ah,24h
    dirmsg db 9,'<dir>',0Dh,0Ah,24h

    hndl dw 0 ; File handle storage.
    buf db 0 ; Dynamic storage. Do not move!
    filename db 'crc1.com',0 ; filename to do a CRC check on

    cseg ends
    end Begin

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