50 lines
815 B
C++
Executable File
50 lines
815 B
C++
Executable File
// $Id: crc32.cpp,v 1.1 2004/07/08 15:21:21 philip Exp $
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#include "precompiled.h"
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// CRC32, based on code copied from anywhere on the internet.
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// Find a thousand possible sources at
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// http://www.google.com/search?q=0xEDB88320L
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unsigned long crc_table[256];
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int generate_table()
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{
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unsigned long crc;
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int i, j;
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const unsigned long poly = 0xEDB88320L; // magic
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for (i = 0; i < 256; ++i)
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{
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crc = i;
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for (j = 0; j < 8; ++j)
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{
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if (crc & 1)
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crc = (crc >> 1) ^ poly;
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else
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crc >>= 1;
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}
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crc_table[i] = crc;
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}
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return 0;
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}
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unsigned long crc32_calculate(char* data, int len)
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{
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// Only calculate the table once
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static int _temp = generate_table();
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unsigned long crc;
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crc = ~0;
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while (len)
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{
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crc = (crc>>8) ^ crc_table[ (crc^*data) & 0xff ];
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--len; ++data;
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}
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return ~crc;
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}
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