CRC32校验C代码

 CRC32校验C代码

来自 http://www.ec66.com/article/list.asp?indexid=4251

 

/* CRC-32b version 1.03 by Craig Bruce, 27-Jan-94
**
** Based on "File Verification Using CRC" by Mark R. Nelson in Dr. Dobb's
** Journal, May 1992, pp. 64-67. This program DOES generate the same CRC
** values as ZMODEM and PKZIP
**
** v1.00: original release.
** v1.01: fixed printf formats.
** v1.02: fixed something else.
** v1.03: replaced CRC constant table by generator function.
*/

#include <stdio.h>

int main();
unsigned long getcrc();
void crcgen();

unsigned long crcTable[256];

/****************************************************************************/
int main( argc, argv )
int argc;
char *argv[];
{
    int i;
    FILE *fp;
    unsigned long crc;

    crcgen();
    if (argc < 2) 
    {
        crc = getcrc( stdin );
        printf("crc32 = %08lx for <stdin>\n", crc);
    }
   else
   {
        for (i=1; i<argc; i++)
        {
            if ( (fp=fopen(argv[i],"rb")) == NULL ) 
            {
                printf("error opening file \"%s\"!\n",argv[i]);
            } 
            else
            {
                crc = getcrc( fp );
                printf("crc32 = %08lx for \"%s\"\n",  crc, argv[i]);
                fclose( fp );
            }
        }
    }
return( 0 );
}

/****************************************************************************/
unsigned long getcrc( fp )
FILE *fp;
{
    register unsigned long crc;
    int c;

    crc = 0xFFFFFFFF;
    while( (c=getc(fp)) != EOF )
    {
        crc = ((crc>>8) & 0x00FFFFFF) ^ crcTable[ (crc^c) & 0xFF ];
    }
    return( crc^0xFFFFFFFF );
}

/****************************************************************************/
void crcgen( )
{
    unsigned long crc, poly;
    int i, j;

    poly = 0xEDB88320L;
    for (i=0; i<256; i++)
    {
        crc = i;
        for (j=8; j>0; j--)
        {
            if (crc&1)
            {
                crc = (crc >> 1) ^ poly;
            }
           else
            {
                crc >>= 1;
            }
        }
        crcTable[i] = crc;
    }
}