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【C】 CRC16计算文件的校验和

作者: / 发布于2014/5/22/ 646

CRC16计算文件的校验和


	#include <stdio.h>
	#include <stdlib.h>
	#define DRIVER 1 /* brings in the main line */
	/* Compute a CRC-16 value */
	unsigned short int GetCRC16 (
	 int start, /* starting value */
	 const char *p, /* points to chars to process */
	 int n ) /* how many chars to process */
	{
	 static unsigned int crcl6_table[16] = /* CRC-16s */
	 {
	 0x0000, 0xCC01, 0xD801, 0x1400,
	 0xF001, 0x3C00, 0x2800, 0xE401,
	 0xA001, 0X6C00, 0x7800, 0xB401,
	 0x5000, 0x9C01, 0x8801, 0x4400
	 };
	 unsigned short int total; /* the CRC-16 value we compute */
	 int r1;
	 total = start;
	 /* process each byte */
	 while ( n-- > 0 )
	 {
	 /* do the lower four bits */
	 r1 = crcl6_table[ total & 0xF ];
	 total = ( total >> 4 ) & 0x0FFF;
	 total = total ^ r1 ^ crcl6_table[ *p & 0xF ];
	 /* do the upper four bits */
	 r1 = crcl6_table[ total & 0xF ];
	 total = ( total >> 4 ) & 0x0FFF;
	 total = total ^ r1 ^ crcl6_table[ ( *p >> 4 ) & 0xF ];
	 /* advance to next byte */
	 p++;
	 }
	 return total;
	}
	#ifdef DRIVER
	#define BUFSIZE 8192
	main ( int argc, char *argv[] )
	{
	 FILE *fin;
	 int n; /* number of bytes actually read */
	 unsigned short int crc; /* CRC value */
	 char *buffer; /* buffer into which we read file */
	 if ( argc < 2 )
	 {
	 fprintf ( stderr, "Error: must provide filename\\n" );
	 return EXIT_FAILURE;
	 }
	 if (( fin = fopen ( argv[1], "rb" )) == NULL )
	 {
	 fprintf ( stderr, "Cannot open %s \\n", argv[1] );
	 return EXIT_FAILURE;
	 }
	 buffer = (char *) malloc ( BUFSIZE );
	 if ( buffer == NULL )
	 {
	 fprintf ( stderr, "Error allocating memory\\n" );
	 return EXIT_FAILURE;
	 }
	 crc = 0;
	 /* principal processing loop */
	 do
	 {
	 /* read file in 8KB blocks */
	 n = fread ( buffer, 1, BUFSIZE, fin );
	 /* Fold in this block&apos;s CRC-16 */
	 crc = GetCRC16 ( crc, buffer, n );
	 }
	 while ( n== BUFSIZE ); /* Stop when done */
	 fclose ( fin ) ;
	 /* check for read error */
	 if ( ferror ( fin ))
	fprintf ( stderr, "Error in Processing %s\\n", argv[1] );
	 /* No error, so report CRC-16 */
	 else
	 printf ( "CRC-16 for %s = %04X\\n", argv[1], crc );
	 return EXIT_SUCCESS;
	}
	#endif

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