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72 lines
2.0 KiB
72 lines
2.0 KiB
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#ifndef _CRC32_H_
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#define _CRC32_H_
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#ifndef INLINE
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#define INLINE __inline
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#endif
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extern const ULONG CrcTable32[ 256 ]; // defined in crctable.c
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VOID GenerateCrc32Table( VOID ); // stubbed in crctable.c, but not used
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// (exists for compatibility)
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ULONG
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INLINE
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Crc32(
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IN ULONG InitialCrc,
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IN PVOID Buffer,
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IN ULONG ByteCount
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)
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{
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#ifdef _X86_
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__asm {
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mov ecx, ByteCount ; number of bytes in buffer
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xor ebx, ebx ; ebx (bl) will be our table index
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mov esi, Buffer ; buffer pointer
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test ecx, ecx ; test for zero length buffer
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mov eax, InitialCrc ; CRC-32 value
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jnz short loopentry ; if non-zero buffer, start loop
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jmp short exitfunc ; else exit (crc already in eax)
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looptop: shr eax, 8 ; (crc>>8) (U1)
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mov edx, CrcTable32[ebx*4] ; fetch Table[ index ] (V1)
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xor eax, edx ; crc=(crc>>8)^Table[index] (U1)
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loopentry: mov bl, [esi] ; fetch next *buffer (V1)
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inc esi ; buffer++ (U1)
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xor bl, al ; index=(byte)crc^*buffer (V1)
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dec ecx ; adjust counter (U1)
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jnz short looptop ; loop while nBytes (V1)
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shr eax, 8 ; remaining math on last byte
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xor eax, CrcTable32[ebx*4] ; eax returns new crc value
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exitfunc:
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}
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#else // ! _X86_
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ULONG Value = InitialCrc;
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ULONG Count = ByteCount;
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PUCHAR p = Buffer;
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while ( Count-- ) {
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Value = ( Value >> 8 ) ^ CrcTable32[ (UCHAR)( *p++ ^ Value ) ];
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}
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return Value;
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#endif // ! _X86_
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}
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#endif // _CRC32_H_
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