/*
** tablecrc -  table lookup crc routines
*/

#include "a:stdio.h"

#define TRUE 1
#define FALSE 0

char Crctbl[512];

main(argc,argv)
int argc;
char **argv;
{
	extern crcgen();
	extern unsigned updcrc();
	
	unsigned crcval;
	int c,i;
	char ch;
	char *crcptr, *xptr;
	FILE *fdi;

	crcgen();				/* generate the crc table */

	if(argc < 2) {
		puts("TABLECRC - calculate crc of a file using table-driven crc");
		printf("Usage: tablecrc infile");
		exit();
	}

	if((fdi = fopen(*++argv,"r")) == NULL) {
		printf("? can't open file %s\n", *argv);
		exit();
	}

	crcval = 0;

	while((c = getc(fdi)) != EOF) {
		ch = c;
		crcval = updcrc(ch, crcval);
	}
	printf("crc = %x Hex\n", crcval);
}


crcgen()
{
	register char *crcptr;
	register int crcval;
	register int c;
	int b;

	crcptr = &Crctbl[0];
	for(c=0; c<256; c++) {
		crcval = (c << 8);
		for(b=0; b<8; b++) {
			if(crcval & 0x8000) {
				crcval = crcval << 1;
				crcval ^= 0x1021;
			}
			else
				crcval = crcval << 1;

		}
		*crcptr = crcval >> 8;
		*(crcptr+256) = crcval & 0xff;
		crcptr++;
	}
}


unsigned updcrc(ch, crcval)
char ch;
unsigned crcval;
{
	register int indx;
	register unsigned msbcrc, lsbcrc;

	indx = ch ^ ((crcval >> 8) & 0xff);
	msbcrc = Crctbl[indx] ^ (crcval & 0xff);
	lsbcrc = Crctbl[indx+256];
	return (unsigned) ((msbcrc << 8) | lsbcrc);
}