145 lines
6.4 KiB
C++
145 lines
6.4 KiB
C++
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// Copyright (c) 1999 Microsoft Corporation. All Rights Reserved.
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#include <streams.h>
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#include "crc32.h"
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//
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// Computes the bit reversed CRC32 polynomial
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//
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// The faster table version. Use the init routine below with the reversed CRC polynomial 0xedb88320 to create it
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// Note: the actual poly is reversed 0xedb88320 but the leading '1' is implied
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// (since X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
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// = %1 0000 0100 1100 0001 0001 1101 1011 0111
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// = 0000 0100 1100 0001 0001 1101 1011 0111 (mod x^32, drop the top bit)
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// reversed:
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// 1110 1101 1011 1000 1000 0011 0010 0000
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// = e d b 8 8 3 2 0
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//
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static const DWORD dwCRC32_LOOKUP_TABLE [] = {
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0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
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0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
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0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
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0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
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0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
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0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
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0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
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0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
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0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
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0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
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0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
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0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
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0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
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0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
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0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
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0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
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0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
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0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
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0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
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0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
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0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
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0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
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0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
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0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
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0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
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0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
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0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
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0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
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0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
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0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
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0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
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0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
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};
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#if 0
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// this is actually calculating the reverse CRC
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// computing the reverse CRC of 0 gives the table entry above
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//
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static uint32 calc_entry( uint32 crc, unsigned index, uint32 poly )
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{
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for(int i=0;i<8;i++)
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{
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if((crc ^ index) & 1)
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crc = (crc>>1)^poly;
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else
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crc>>= 1;
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index >>= 1;
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}
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return crc;
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}
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static void initcrc32table( uint32 poly, uint32 CrcXorTable[256] )
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{
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for (unsigned i = 0; i < 256; ++i) {
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uint32 entry = calc_entry( 0, i, poly );
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CrcXorTable[i] = entry;
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// print out for embedding the table
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Dbg( logTrace(2) << dm_hex( CrcXorTable[i] ) << ", " );
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if( (i & 3) == 3 ) {
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Dbg( logTrace(2) << dm_endl );
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}
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}
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}
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#endif
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static inline DWORD NewCRC32(DWORD crc, BYTE bNextByte )
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{
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// #define UPDC32(table, b, crc) (table[((int)crc ^ b) & 0xff] ^ ((crc >> 8) & 0x00FFFFFF))
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return dwCRC32_LOOKUP_TABLE[ BYTE(crc ^ bNextByte) ] ^ (crc >> 8);
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}
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DWORD CRC32::Update( BYTE bNextByte )
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{
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m_crc32 = NewCRC32(m_crc32, bNextByte);
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return m_crc32;
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}
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DWORD CRC32::Update( const void* pBuffer, unsigned uLength )
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{
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// modifies the current state
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DWORD dwCurrentCRC32 = m_crc32;
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const BYTE* pByte= (const BYTE*)pBuffer;
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for(; uLength > 4; uLength-=4 ) {
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// constant unrolling 4x dramatically helps the crc code
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// beyond that there's not much gain
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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}
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// finish up the remainder
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for(; uLength > 0; uLength-- ) {
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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}
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m_crc32 = dwCurrentCRC32;
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return dwCurrentCRC32;
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}
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// This function is nearly identical, but we win out on a few assignments
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// This is done for some speed (can avoid assigning m_crc32 several times)
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CRC32::CRC32(const void* pPtr, unsigned uLength)
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{
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// do not rely on the optimizer to treat m_crc32 as a local variable
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// assigned at the end
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DWORD dwCurrentCRC32 = 0xffffffff;
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const BYTE* pByte= (const BYTE*)pPtr;
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for(; uLength > 4; uLength-=4 ) {
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// constant unrolling 4x dramatically helps the crc code
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// beyond that there's not much gain
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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}
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// finish up the remainder
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for(; uLength > 0; uLength-- ) {
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dwCurrentCRC32 = NewCRC32(dwCurrentCRC32, *pByte++);
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}
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m_crc32 = dwCurrentCRC32;
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}
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