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flat assembler > Macroinstructions > How to store 32bit (or more) CRC @end of file @compile time?

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Matrix



Joined: 04 Sep 2004
Posts: 1171
Location: Overflow
Hy,
can someone give me a hint on some macro?
i'd like to store my executable's 32bit crc @ the end so i can later verify it during runtime, and see if any modifications were made.
thnx
Post 08 Nov 2004, 18:56
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decard



Joined: 11 Sep 2003
Posts: 1095
Location: Poland
quick dirty solution, but you should be able to modify it that it would fit your needs.
Code:
macro generate_crc starting_lbl, ending_lbl {
  __ptr = starting_lbl
  __times = (ending_lbl-starting_lbl)/4
  __sum = 0
  repeat __times
    load __tmp dword from __ptr
    __sum = __sum + __tmp
    __ptr = __ptr + 4
  end repeat
  dd __sum and 0xffffffff
}    


it will store dword value that would be a sum of all dwords in the output code, between two given labels. Example:
Code:
begin:
     dd 11
     dd 2
     dd 2
finish:

db "CRC:"
generate_crc begin,finish    
Post 08 Nov 2004, 19:17
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Matrix



Joined: 04 Sep 2004
Posts: 1171
Location: Overflow
Thank you Decard Smile
Post 08 Nov 2004, 19:32
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Matrix



Joined: 04 Sep 2004
Posts: 1171
Location: Overflow
Here is what i did with it, not much modification was needed Smile
now works with any block size
well exacly this is not a full crc32, but it should be enough for me now

Code:
macro generate_crc starting_lbl, ending_lbl {
  __ptr = starting_lbl
  __lenght = ending_lbl-starting_lbl
  __times = (__lenght)shr 2
  __timesleft = (__lenght)-(((__lenght)shr 2)shl 2) ; remaining 3 - 0
  __timesleft2 =__timesleft shr 1 ; word
  __timesleft3 =__timesleft - (__timesleft2 shl 1) ; last byte

  __sum = 0
  repeat __times
    load __tmp dword from __ptr
    __sum = __sum xor __tmp
    __ptr = __ptr + 4
  end repeat
    if __timesleft2>0   ; word
    load __tmp word from __ptr
    __sum = __sum xor (__tmp and $ffff)
    __ptr = __ptr + 2
    end if
    if __timesleft3>0 ; last byte
    load __tmp byte from __ptr
    __sum = __sum xor (__tmp and $ff)
    __ptr = __ptr + 1
    end if

  dd __sum and 0xffffffff
}

;it will store dword value that would be a sum of all dwords in the output code, between two given labels. Example:
;Code:

     dd $ABCD
begin:
     dd 10101010101010101010101010101010b
     dd 11111111111111111111111111111111b
     dd 11111111111111111111111111111111b
     dd 10101010101010101010111010101010b
     db 1b,0
;     dw 1b
;     dw 0
;     dw 100000001b

finish:

db "CRC:"
generate_crc begin,finish

    
Post 08 Nov 2004, 19:42
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