1/*
2 * efone - Distributed internet phone system.
3 *
4 * (c) 1999,2000 Krzysztof Dabrowski
5 * (c) 1999,2000 ElysiuM deeZine
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version
10 * 2 of the License, or (at your option) any later version.
11 *
12 */
13
14/* based on implementation by Finn Yannick Jacobs */
15
16#include <stdio.h>
17#include <stdlib.h>
18#include <sys/types.h>
19#include "crc32.h"
20
21/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
22 *		so make sure, you call it before using the other
23 *		functions!
24 */
25uint32_t crc_tab[256];
26
27/* chksum_crc() -- to a given block, this one calculates the
28 *				crc32-checksum until the length is
29 *				reached. the crc32-checksum will be
30 *				the result.
31 */
32uint32_t chksum_crc32 (unsigned char *block, unsigned int length)
33{
34   unsigned long crc;
35   unsigned long i;
36
37   crc = 0xFFFFFFFF;
38   for (i = 0; i < length; i++)
39   {
40      crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
41   }
42   return (crc ^ 0xFFFFFFFF);
43}
44
45/* chksum_crc32gentab() --      to a global crc_tab[256], this one will
46 *				calculate the crcTable for crc32-checksums.
47 *				it is generated to the polynom [..]
48 */
49
50void chksum_crc32gentab ()
51{
52   unsigned long crc, poly;
53   int i, j;
54
55   poly = 0xEDB88320L;
56   for (i = 0; i < 256; i++)
57   {
58      crc = i;
59      for (j = 8; j > 0; j--)
60      {
61	 if (crc & 1)
62	 {
63	    crc = (crc >> 1) ^ poly;
64	 }
65	 else
66	 {
67	    crc >>= 1;
68	 }
69      }
70      crc_tab[i] = crc;
71   }
72}
73