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// Calculate a CRC 32 checksum.
#include <malloc.h>
#include <stdio.h>
// LAST MODIFIED:[7-28-93]
// Usage:
// unsigned long crc = -1L
// crc = crc32(buffer, length, crc)
unsigned long crc32 (void *buffer, unsigned int count, unsigned long crc);
static int BuildCRCTable (void);
static unsigned long *CRCTable; // Table constructed for fast lookup.
#define CRC32_POLYNOMIAL 0xEDB88320L
// Initialize the CRC calculation table
//
static int
BuildCRCTable (void)
{
int i, j;
unsigned long crc;
CRCTable = malloc (256 * sizeof (unsigned long));
if (CRCTable == NULL)
{
fprintf (stderr, "Can't malloc space for CRC table in file %s\n",
__FILE__);
return -1L;
}
for (i = 0; i <= 255; i++)
{
crc = i;
for (j = 8; j > 0; j--)
if (crc & 1)
crc = (crc >> 1) ^ CRC32_POLYNOMIAL;
else
crc >>= 1;
CRCTable[i] = crc;
}
return 0;
}
unsigned long
crc32 (void *buffer, unsigned int count, unsigned long crc)
{
unsigned long temp1, temp2;
static int firsttime = 1;
unsigned char *p = (unsigned char *) buffer;
if (firsttime)
{
if (BuildCRCTable ())
return -1;
firsttime = 0;
}
while (count-- != 0)
{
temp1 = (crc >> 8) & 0x00FFFFFFL;
temp2 = CRCTable[((int) crc ^ *p++) & 0xFF];
crc = temp1 ^ temp2;
}
return crc;
}
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