76 lines
1.2 KiB
C++
76 lines
1.2 KiB
C++
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/*++
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Copyright (c) 1998-1999, Microsoft Corporation
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Module Name:
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Crc32.cpp
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Abstract:
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--*/
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#include "Crc32.h"
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CCrc32::CCrc32()
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{
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uClassID = CCRC32_CLASSID;
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InitialiseCRCTable();
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}
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CCrc32::~CCrc32()
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{
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}
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VOID CCrc32::InitialiseCRCTable()
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{
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INT nIndex;
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INT nBitIndex;
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ULONG uTableValue;
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for ( nIndex = 0; nIndex < 256; nIndex++ )
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{
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uTableValue = nIndex;
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for ( nBitIndex = 0; nBitIndex < 8; nBitIndex++ )
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{
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if ( ( uTableValue & 1 ) == 1 )
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{
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uTableValue = ( uTableValue >> 1 ) ^ CRC32_POLYNOMIAL;
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} else
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{
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uTableValue = uTableValue >> 1;
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}
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}
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m_uCRC32Table[ nIndex ] = uTableValue;
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}
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}
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ULONG CCrc32::CalculateBlockCRC(LPVOID lpvBlock, INT nBlockLength)
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{
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INT nIndex;
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LPBYTE lpbBlock;
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ULONG uCRCValue;
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_ASSERT( nBlockLength > 0 );
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lpbBlock = (LPBYTE)lpvBlock;
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uCRCValue = 0xFFFFFFFFL;
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for ( nIndex = 0; nIndex < nBlockLength; nIndex++ )
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{
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uCRCValue = ( ( uCRCValue >> 8 ) & 0x00FFFFFFL ) ^ ( m_uCRC32Table[ ( uCRCValue ^ lpbBlock[ nIndex ] ) & 0xFFL ] );
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}
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uCRCValue = uCRCValue ^ 0xFFFFFFFFL;
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return uCRCValue;
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}
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