source: liacs/alg/solitaire/crc/lib_crc.c@ 6

Last change on this file since 6 was 2, checked in by Rick van der Zwet, 15 years ago

Initial import of data of old repository ('data') worth keeping (e.g. tracking
means of URL access statistics)
  • Property svn:executable set to *
File size: 2.2 KB
RevLine 
[2]1#include "lib_crc.h"
2#define P_32 0xEDB88320L
3
4static int crc_tab32_init = FALSE;
5
6static unsigned long crc_tab32[256];
7
8
9static void init_crc32_tab( void );
10
11
12 /*******************************************************************\
13 * *
14 * unsigned long update_crc_32( unsigned long crc, char c ); *
15 * *
16 * The function update_crc_32 calculates a new CRC-32 value *
17 * based on the previous value of the CRC and the next byte *
18 * of the data to be checked. *
19 * *
20 \*******************************************************************/
21
22unsigned long update_crc_32( unsigned long crc, char c ) {
23
24 unsigned long tmp, long_c;
25
26 long_c = 0x000000ffL & (unsigned long) c;
27
28 if ( ! crc_tab32_init ) init_crc32_tab();
29
30 tmp = crc ^ long_c;
31 crc = (crc >> 8) ^ crc_tab32[ tmp & 0xff ];
32
33 return crc;
34
35} /* update_crc_32 */
36
37
38 /*******************************************************************\
39 * *
40 * static void init_crc32_tab( void ); *
41 * *
42 * The function init_crc32_tab() is used to fill the array *
43 * for calculation of the CRC-32 with values. *
44 * *
45 \*******************************************************************/
46
47static void init_crc32_tab( void ) {
48
49 int i, j;
50 unsigned long crc;
51
52 for (i=0; i<256; i++) {
53
54 crc = (unsigned long) i;
55
56 for (j=0; j<8; j++) {
57
58 if ( crc & 0x00000001L ) crc = ( crc >> 1 ) ^ P_32;
59 else crc = crc >> 1;
60 }
61
62 crc_tab32[i] = crc;
63 }
64
65 crc_tab32_init = TRUE;
66
67} /* init_crc32_tab */
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