crc1

/* compute crc's */
/* crc-ccitt is based on the polynomial x^16+x^12+x^5+1 */
/* The prescription for determining the mask to use for a given polynomial
    is as follows:
        1.  Represent the polynomial by a 17-bit number
        2.  Assume that the most and least significant bits are 1
        3.  Place the right 16 bits into an integer
*/
/* Usage : ccitt [filename] */

#include    <stdio.h>
#include    <stdlib.h>
#include    <string.h>
#include    <time.h>

#define     MTT 0x8000000200021013L     /* crc-ccitt mask */
#define     CLK_TCK CLOCKS_PER_SEC

/* function declarations */
void updcrc(unsigned long long*,unsigned long long,unsigned long long);
void perr(char *);

/* variables */
char filename[100];
unsigned long long crctt[2];
unsigned long long ch;
unsigned long num;
FILE *fp;

/* driver */
int main(argc,argv)
int argc; char **argv;
{
 clock_t start,end;
    if(argc>2) perr("Usage:  ccitt [filename]");
    if(argc==2) strcpy(filename,argv[1]);
    else
    {
        printf("\nEnter filename:  ");
        gets(filename);
    }
    if((fp=fopen(filename,"rb"))==NULL) perr("Can't open file");
    num=0L; crctt[0]=0, crctt[1]=0;
    start=clock();
    //printf("%d\n", sizeof(unsigned long long));

    while((ch=fgetc(fp))!=EOF)
    {
        //if (ch == '\n')
        //  continue;
        num++;
        //int i; for (i=0;i<10000;i++){
        updcrc(crctt,ch,MTT);
        //}
    }
    crctt[0]%=(1<<10);
    end=clock();
    fclose(fp);
    printf("\nNumber of bytes = %lu\n CRCTT = %llX%llX\n", num, crctt[0], crctt[1]);
    printf("Czas trwania: %f\n",(double)(end-start)/CLK_TCK);
    return 0;
}

/* update crc */
void updcrc(crc,c,mask)
unsigned long long *crc, c, mask;
{
    int i;
    c<<=2;
    for(i=0;i<8;i++)
    {
        if((crc[0] ^ c) & (1<<9))
        {
            crc[0]<<=1;
            if(crc[1]&(1LLU<<63))
                crc[0]+=1;
            crc[1]=(crc[1]<<1)^mask;
            crc[0]=crc[0]^0LLU;
        }
        else
        {
            crc[0]<<=1;
            if(crc[1]&(1LLU<<63))
                crc[0]+=1;
            crc[1]<<=1;
        }
        c<<=1;
    }
}

/* error abort */
void perr(s)
char *s;
{
    printf("\n%s",s); exit(1);
}