/* generate crc tables for crc-16 and crc-ccitt */
/* crc-16 is based on the polynomial x^16+x^15+x^2+1 */
/*  The bits are inserted from least to most significant */
/* crc-ccitt is based on the polynomial x^16+x^12+x^5+1 */
/*  The bits are inserted from most to least significant */
/* 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
                4.  Bit reverse if serial LSB's are sent first
*/

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

#define         M16     0xA001          /* crc-16 mask */
#define         MTT     0x1021          /* crc-ccitt mask */

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

/* driver */
main()
{
        int i,j;
        printf("\n\t");
        for(i=0;i<32;i++)
        {
                for(j=0;j<8;j++) printf("0x%04X, ",updcrcr(0,8*i+j,M16));
                printf("\n\t");
        }
        printf("\n\t");
        for(i=0;i<32;i++)
        {
                for(j=0;j<8;j++) printf("0x%04X, ",updcrc(0,8*i+j,MTT));
                printf("\n\t");
        }
}

/* update crc */
unsigned int updcrc(unsigned int crc,int c,unsigned int mask)
{
        int i;
        c<<=8;
        for(i=0;i<8;i++)
        {
                if((crc ^ c) & 0x8000) crc=(crc<<1)^mask;
                else crc<<=1;
                c<<=1;
        }
        return crc;
}

/* update crc reverse */
unsigned int updcrcr(unsigned int crc,int c,unsigned int mask)
{
        int i;
        for(i=0;i<8;i++)
        {
                if((crc ^ c) & 1) crc=(crc>>1)^mask;
                else crc>>=1;
                c>>=1;
        }
        return crc;
}

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