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Last change
on this file since 200 was 2, checked in by Rick van der Zwet, 15 years ago |
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Initial import of data of old repository ('data') worth keeping (e.g. tracking
means of URL access statistics)
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-
Property svn:executable
set to
*
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File size:
2.2 KB
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| 1 | #include "lib_crc.h"
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| 2 | #define P_32 0xEDB88320L
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| 3 |
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| 4 | static int crc_tab32_init = FALSE;
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| 5 |
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| 6 | static unsigned long crc_tab32[256];
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| 7 |
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| 8 |
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| 9 | static void init_crc32_tab( void );
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| 10 |
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| 11 |
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| 12 | /*******************************************************************\
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| 13 | * *
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| 14 | * unsigned long update_crc_32( unsigned long crc, char c ); *
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| 15 | * *
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| 16 | * The function update_crc_32 calculates a new CRC-32 value *
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| 17 | * based on the previous value of the CRC and the next byte *
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| 18 | * of the data to be checked. *
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| 19 | * *
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| 20 | \*******************************************************************/
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| 21 |
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| 22 | unsigned long update_crc_32( unsigned long crc, char c ) {
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| 23 |
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| 24 | unsigned long tmp, long_c;
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| 25 |
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| 26 | long_c = 0x000000ffL & (unsigned long) c;
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| 27 |
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| 28 | if ( ! crc_tab32_init ) init_crc32_tab();
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| 29 |
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| 30 | tmp = crc ^ long_c;
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| 31 | crc = (crc >> 8) ^ crc_tab32[ tmp & 0xff ];
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| 32 |
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| 33 | return crc;
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| 34 |
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| 35 | } /* update_crc_32 */
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| 36 |
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| 37 |
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| 38 | /*******************************************************************\
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| 39 | * *
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| 40 | * static void init_crc32_tab( void ); *
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| 41 | * *
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| 42 | * The function init_crc32_tab() is used to fill the array *
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| 43 | * for calculation of the CRC-32 with values. *
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| 44 | * *
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| 45 | \*******************************************************************/
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| 46 |
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| 47 | static void init_crc32_tab( void ) {
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| 48 |
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| 49 | int i, j;
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| 50 | unsigned long crc;
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| 51 |
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| 52 | for (i=0; i<256; i++) {
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| 53 |
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| 54 | crc = (unsigned long) i;
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| 55 |
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| 56 | for (j=0; j<8; j++) {
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| 57 |
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| 58 | if ( crc & 0x00000001L ) crc = ( crc >> 1 ) ^ P_32;
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| 59 | else crc = crc >> 1;
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| 60 | }
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| 61 |
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| 62 | crc_tab32[i] = crc;
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| 63 | }
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| 64 |
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| 65 | crc_tab32_init = TRUE;
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| 66 |
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| 67 | } /* init_crc32_tab */
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