/*
 *  crc8.c - 8ビットCRCの計算
 *
 *  revision history:
 *	0.0: Dec. 16, 2021 by Dai ISHIJIMA
 *
 *  参考文献:
 *      W.H.Press, et al.: Numerical Recipes in C
 *      (Cambridge University Press, 1992) 2nd ed., pp.896-901.
 */

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>	/* strtol(3) */

#define EOS '\0'

#define shift --argc; ++argv
char *prog;


/*				   8 7654 3210 		dallas-maxim */
#define GX 0x131		/* 1 0011 0001: G(x) = x^8 + x^5 + x^4 + 1 */
#define INI 0xff		/* initial value */

#define P ((GX) & 0xff)		/* Polynomial */


unsigned char rawcrc8(unsigned char p, unsigned char crc, unsigned char ch)
{
    int bit;

    crc ^= ch;
    for (bit = 0; bit < 8; bit++) {
	if (crc & 0x80) {
	    crc <<= 1;
	    crc ^= p;
	}
	else {
	    crc <<= 1;
	}
    }
    return(crc);
}


unsigned char crc8s(unsigned char ini, unsigned char p,
		    int len, unsigned char *s)
{
    int i;
    unsigned char crc;

    crc = ini;
    for (i = 0; i < len; i++) {
	crc = rawcrc8(p, crc, s[i]);
    }
    return(crc);
}


void calc(FILE *fp, int p, int ini)
{
    int len;
    unsigned char buf[BUFSIZ];

    if ((len = fread(buf, 1, BUFSIZ - 1, fp)) > 0) {
	printf("%02x\n", crc8s(ini, p, len, buf));
    }
}


void usage()
{
    fprintf(stderr, "Usage: %s [options] [file]\n", prog);
    fprintf(stderr, "    options:\n");
    fprintf(stderr, "\t-g GX (HEX) / -G GX (DEC)\n");
    fprintf(stderr, "\t-p polynomial (HEX) / -p polynomial (DEC)\n");
    fprintf(stderr, "\t-i initial value (HEX) / -I initial value (DEC)\n");
    fprintf(stderr, "    example:\n");
    fprintf(stderr, "\t%s -g 0x131 -i 0xff dallas-maxim.dat\n", prog);
    fprintf(stderr, "\t%s -g 0x185 -i 0 x8+x7+x2+1.dat\n", prog);

}


int main(int argc, char *argv[])
{
    FILE *fp;
    int p, ini;

    prog = *argv;
    shift;
    p = P;
    ini = INI;
    while ((argc > 0) && (argv[0][0] == '-') && (argv[0][1] != EOS)) {
	if ((argc > 1) && (argv[0][1] == 'p')) {
	    shift;
	    p = strtol(*argv, (char **)NULL, 16) & 0xff;
	}
	else if ((argc > 1) && (argv[0][1] == 'P')) {
	    shift;
	    p = atoi(*argv) & 0xff;
	}
	else if ((argc > 1) && (argv[0][1] == 'g')) {
	    shift;
	    p = strtol(*argv, (char **)NULL, 16) & 0xff;
	}
	else if ((argc > 1) && (argv[0][1] == 'G')) {
	    shift;
	    p = atoi(*argv) & 0xff;
	}
	else if ((argc > 1) && (argv[0][1] == 'i')) {
	    shift;
	    ini = strtol(*argv, (char **)NULL, 16) & 0xff;
	}
	else if ((argc > 1) && (argv[0][1] == 'I')) {
	    shift;
	    ini = atoi(*argv) & 0xff;
	}
	else {
	    usage();
	    exit(1);
	}
	shift;
    }
    if (argc > 0) {
	while (argc > 0) {
	    if ((argv[0][1] == '-') && (argv[0][1] == EOS)) {
		fp = stdin;
	    }
	    else if ((fp = fopen(*argv, "r")) == NULL) {
		fprintf(stderr, "%s: can't open %s\n", prog, *argv);
		exit(1);
	    }
	    calc(fp, p, ini);
	    if (fp != stdin) {
		fclose(fp);
	    }
	    shift;
	}
    }
    else {
	calc(stdin, p, ini);
    }
    exit(0);
}

/* Local Variables: */
/* compile-command:"cc -Wall -o crc8 crc8.c" */
/* End: */