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【C】动态计算CRC-CCITT

作者:DDT / 发布于2012/7/16/ 521

整个文件一次一字节地动态计算CRC-CCITT

#include <stdio.h> 
#include <stdlib.h>
#define DRIVER 1 /* DRIVER includes the file processing */
/* Compute single-byte CRC-CCITT on-the-fly */
unsigned short GetCCITT ( unsigned short crc, unsigned short ch ) 
{
static unsigned int i;
ch <<= 8;	/* Move to MSB	*/
for ( i = 8; i > 0; i-- )	/* Go through 8 bits */
{
if ( (ch ^ crc) & 0x8000 ) /* Perform CRC calc. */ 
crc = ( crc << 1 ) ^ 0x1021;
else
crc<<=1;
ch<<=1;
}
return crc;
}
#ifdef DRIVER
int main ( int argc, char * argv[] )
{
FILE *fin;	/* file we're reading into buffer */
char *buffer;	/* buffer we're working on	*/
size_t i,j;	/* counters of bytes in buff	*/
unsigned short crc; /* the CRC value being computed */
if ( argc < 2 )
{
fprintf ( stderr, "Error! Must specify filename.\n" ); 
return EXIT_FAILURE;
}
if (( fin = fopen ( argv[1], "rb" )) == NULL )
{
fprintf ( stderr, "Cannot open %s", argv[1] );
return EXIT_FAILURE;
}
if (( buffer = (char *) malloc ( 32766 )) == NULL )
{
fprintf ( stderr, "Out of memory\n" );
return EXIT_FAILURE;
}
crc = 0;
for (;;)
{
i = fread ( buffer, 1, 32766, fin );
if ( i == 0 )
{
if ( feof ( fin )) /* we're done, so show results */
{
printf ( "CCITT CRC for %s is %04X\n",argv[1], crc );
return EXIT_SUCCESS;
}
else	/* read another 32K of file */
continue;
}
for (j=0;j<i;j++) /* loop through the buffer */ 
crc = GetCCITT ( crc, buffer [j] );
}
}
#endif</div>

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