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;; Copyright (C) KolibriOS team 2004-2024. All rights reserved. ;;

;;  Distributed under terms of the GNU General Public License.  ;;

;;                                                              ;;

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; This crc32 routine doesn't use precomputed table to allow different

; polynomials, which is the first param.

; Partial hash in assumed to be eax (both in and out).

; Usage:

; 1. mov eax, -1

; 2. stdcall crypto.crc32 zero or more times

; 3. xor eax, -1

proc crc_32 _poly, _buffer, _length

        push    ebx ecx edx esi

        mov     esi, [_buffer]

.next_byte:

        dec     [_length]

        js      .done

        movzx   ebx, byte[esi]

        inc     esi

        mov     ecx, 8

.next_bit:

        mov     edx, eax

        xor     edx, ebx

        shr     eax, 1

        test    edx, 1

        jz      @f

        xor     eax, [_poly]

@@:

        shr     ebx, 1

        dec     ecx

        jnz     .next_bit

        jmp     .next_byte

.done:

        pop     esi edx ecx ebx

        ret

endp