66 lines
1.3 KiB
C
66 lines
1.3 KiB
C
// Calculate a CRC 32 checksum.
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#include <lladd/crc32.h> /*Added 10-6-04 */
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#include <malloc.h>
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#include <stdio.h>
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// LAST MODIFIED:[7-28-93]
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// Usage:
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// unsigned long crc = -1L
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// crc = crc32(buffer, length, crc)
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unsigned int crc32(const void *buffer, unsigned int count, unsigned int crc);
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static int BuildCRCTable(void);
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static unsigned long *CRCTable; // Table constructed for fast lookup.
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#define CRC32_POLYNOMIAL 0xEDB88320
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// Initialize the CRC calculation table
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//
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static int BuildCRCTable(void)
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{
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int i, j;
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unsigned int crc;
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CRCTable = malloc(256 * sizeof(unsigned int));
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if (CRCTable == NULL)
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{
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fprintf(stderr, "Can't malloc space for CRC table in file %s\n", __FILE__);
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return -1L;
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}
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for (i = 0; i <= 255; i++)
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{
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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) ^ CRC32_POLYNOMIAL;
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else
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crc >>= 1;
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CRCTable[i] = crc;
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}
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return 0;
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}
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/* changed long to int, void to const void - rusty. */
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unsigned int crc32(const void *buffer, unsigned int count, unsigned int crc)
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{
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unsigned int temp1, temp2;
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static int firsttime = 1;
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unsigned char *p = (unsigned char *)buffer;
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if (firsttime)
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{
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if (BuildCRCTable())
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return -1;
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firsttime = 0;
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}
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while (count-- != 0)
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{
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temp1 = (crc >> 8) & 0x00FFFFFF;
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temp2 = CRCTable[((int)crc ^ *p++) & 0xFF];
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crc = temp1 ^ temp2;
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}
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return crc;
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}
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