64 lines
1.5 KiB
C
64 lines
1.5 KiB
C
/*
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* efone - Distributed internet phone system.
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*
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* (c) 1999,2000 Krzysztof Dabrowski
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* (c) 1999,2000 ElysiuM deeZine
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* based on implementation by Finn Yannick Jacobs
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*/
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#include <stdio.h>
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#include <stdlib.h>
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/* crc_tab[]
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* this crcTable is being build by chksum_crc32GenTab().
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* so make sure, you call it before using the other
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* functions!
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*/
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u_int32_t crc_tab[256];
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/* chksum_crc()
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* to a given block, this one calculates the
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* crc32-checksum until the length is
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* reached. the crc32-checksum will be
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* the result.
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*/
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u_int32_t chksum_crc32 (unsigned char *block, unsigned int length) {
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register unsigned long crc;
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unsigned long i;
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crc = 0xFFFFFFFF;
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for (i = 0; i < length; i++) {
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crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
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}
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return (crc ^ 0xFFFFFFFF);
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}
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/* chksum_crc32gentab()
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* to a global crc_tab[256], this one will
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* calculate the crcTable for crc32-checksums.
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* it is generated to the polynom [..]
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*/
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void chksum_crc32gentab () {
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unsigned long crc, poly;
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int i, j;
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poly = 0xEDB88320L;
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for (i = 0; i < 256; i++) {
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crc = i;
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for (j = 8; j > 0; j--) {
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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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}
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crc_tab[i] = crc;
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}
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}
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