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gptfdisk/crc32.cc
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/* | |
* 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> | |
#include <sys/types.h> | |
#include "crc32.h" | |
/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab(). | |
* so make sure, you call it before using the other | |
* functions! | |
*/ | |
uint32_t 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. | |
*/ | |
uint32_t 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; | |
} | |
} |