134 lines
2.6 KiB
NASM
134 lines
2.6 KiB
NASM
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; Command & Conquer Red Alert(tm)
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; Copyright 2025 Electronic Arts Inc.
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;
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; This program is free software: you can redistribute it and/or modify
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; it under the terms of the GNU General Public License as published by
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; the Free Software Foundation, either version 3 of the License, or
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; (at your option) any later version.
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;
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; This program is distributed in the hope that it will be useful,
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; but WITHOUT ANY WARRANTY; without even the implied warranty of
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; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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; GNU General Public License for more details.
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;
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; You should have received a copy of the GNU General Public License
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; along with this program. If not, see <http://www.gnu.org/licenses/>.
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;
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;****************************************************************************
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;*
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;* C O N F I D E N T I A L --- W E S T W O O D S T U D I O S
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;*
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;*---------------------------------------------------------------------------
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;*
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;* FILE
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;* crc.asm
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;*
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;* DESCRIPTION
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;* CRC checksum calculation.
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;*
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;* PROGRAMMER
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;* Joe L. Bostic
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;*
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;* DATE
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;* January 26, 1995
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;*
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;*---------------------------------------------------------------------------
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;*
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;* PUBLIC
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;* Calculate_CRC - Calculate CRC checksum.
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;*
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;****************************************************************************
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IDEAL
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P386
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MODEL USE32 FLAT
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LOCALS ??
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CODESEG
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;****************************************************************************
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;*
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;* NAME
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;* Calculate_CRC - Calculate CRC checksum.
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;*
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;* SYNOPSIS
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;* CRC = Calculate_CRC(Buffer, Length)
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;*
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;* long Calculate_CRC(void *, long);
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;*
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;* FUNCTION
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;* Compute a CRC checksum for a block of memory.
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;*
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;* INPUTS
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;* Buffer - Pointer to buffer to calculate CRC for.
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;* Length - Length of buffer.
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;*
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;* RESULT
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;* CRC - CRC value.
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;*
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;****************************************************************************
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GLOBAL C Calculate_CRC:NEAR
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PROC Calculate_CRC C NEAR USES esi ebx ecx edx
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ARG buffer:NEAR PTR
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ARG length:DWORD
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mov esi,[buffer]
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cld
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; Clear CRC to default (NULL) value.
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xor ebx,ebx
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mov ecx,[length] ;Get length of data block
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or ecx,ecx
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jz short ??fini
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; Prepare the length counters.
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mov edx,ecx
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and dl,011b
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shr ecx,2
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; Perform the bulk of the CRC scanning.
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or ecx,ecx
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jz short ??remainder
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??accumloop:
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lodsd
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rol ebx,1
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add ebx,eax
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loop ??accumloop
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; Handle the remainder bytes.
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??remainder:
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or dl,dl
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jz short ??fini
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mov ecx,edx
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xor eax,eax
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push ecx
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??nextbyte:
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lodsb
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ror eax,8
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loop ??nextbyte
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pop ecx
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neg ecx
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add ecx,4
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shl ecx,3
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ror eax,cl
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;??nextbyte:
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; shl eax,8
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; lodsb
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; loop ??nextbyte
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rol ebx,1
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add ebx,eax
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??fini:
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mov eax,ebx
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ret
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ENDP Calculate_CRC
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END
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