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crc.cpp
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crc.cpp
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#define WIN32_LEAN_AND_MEAN
/*
* efone - Distributed internet phone system.
*
* (c) 1999,2000 Krzysztof Dabrowski
* (c) 1999,2000 ElysiuM deeZine
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
*/
/* based on implementation by Finn Yannick Jacobs */
#include <stdio.h>
#include <stdlib.h>
/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
* so make sure, you call it before using the other
* functions!
*/
unsigned int crc_tab[256];
/* chksum_crc() -- to a given block, this one calculates the
* crc32-checksum until the length is
* reached. the crc32-checksum will be
* the result.
*/
unsigned int chksum_crc32 (unsigned char *block, unsigned int length)
{
register unsigned long crc;
unsigned long i;
crc = 0xFFFFFFFF;
for (i = 0; i < length; i++)
{
crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
}
return (crc ^ 0xFFFFFFFF);
}
/* chksum_crc32gentab() -- to a global crc_tab[256], this one will
* calculate the crcTable for crc32-checksums.
* it is generated to the polynom [..]
*/
void chksum_crc32gentab ()
{
unsigned long crc, poly;
int i, j;
poly = 0xEDB88320L;
for (i = 0; i < 256; i++)
{
crc = i;
for (j = 8; j > 0; j--)
{
if (crc & 1)
{
crc = (crc >> 1) ^ poly;
}
else
{
crc >>= 1;
}
}
crc_tab[i] = crc;
}
}
#ifdef TEST
int main(int argc, char *argv[]) {
char *buf = "This is a test buffer.";
chksum_crc32gentab ();
printf("Crc32 %X\n", chksum_crc32(buf, strlen(buf)));
}
#endif