76 lines
1.9 KiB
C++
76 lines
1.9 KiB
C++
#ifndef _CRC32_H_
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#define _CRC32_H_
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class CRC32 {
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public:
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CRC32() {
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InitCRC32Table();
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Reset();
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}
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virtual ~CRC32() {}
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void Reset() {
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m_currentCRC32 = 0xFFFFFFFF;
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}
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void ProcessBuffer(unsigned char* pBuffer, int bufferSize, int stride) {
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// Perform the algorithm on each character
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// in the string, using the lookup table values.
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while(bufferSize > 0) {
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m_currentCRC32 = (m_currentCRC32 >> 8) ^ m_crc32Table[(m_currentCRC32 & 0xFF) ^ *pBuffer];
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pBuffer += stride;
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bufferSize -= stride;
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}
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}
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unsigned int GetCRC() {
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// Exclusive OR the result with the beginning value.
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return m_currentCRC32 ^ 0xFFFFFFFF;
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}
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private:
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// This is the official polynomial used by CRC-32
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// in PKZip, WinZip and Ethernet.
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static const unsigned int Polynomial = 0x04c11db7;
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static const unsigned int CRC32TableSize = 256;
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unsigned int m_crc32Table[CRC32TableSize]; // Lookup table array
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unsigned int m_currentCRC32;
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void InitCRC32Table() {
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// 256 values representing ASCII character codes.
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for(int i = 0; i <= CRC32TableSize; i++) {
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m_crc32Table[i] = Reflect(i, 8) << 24;
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for (unsigned int j = 0; j < 8; j++) {
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m_crc32Table[i] = (m_crc32Table[i] << 1) ^ (m_crc32Table[i] & (1 << 31) ? Polynomial : 0);
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}
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m_crc32Table[i] = Reflect(m_crc32Table[i], 32);
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}
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}
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unsigned int Reflect(unsigned int ref, unsigned char numBits) {
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unsigned int value = 0;
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// Swap bit 0 for bit 7
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// bit 1 for bit 6, etc.
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for(unsigned char i = 1; i < (numBits + 1); i++) {
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if(ref & 1) {
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value |= 1 << (numBits - i);
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}
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ref >>= 1;
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}
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return value;
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}
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};
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#endif
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