/*
	prchksum.c - print checksum for a file.

	Originally coded by folks at Digi
	Corrected for byte-wide variables by Kees Cook <kees@outflux.net>
	Feb 13, 2001

# Copyright (C) 2001 Kees Cook
# kees@outflux.net, http://outflux.net/
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public Licen
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  0211
# http://www.gnu.org/copyleft/gpl.html


*/

#include <stdio.h>


main(argc,argv)
char **argv;
{
	FILE *fp;
	int index;
	int wordflag=0;
	int c,v,sum,last,mask;
	
	index = 1;
	if(argc > 2) {
		if(argv[1][0] != '-')
			usage();
		if(argv[1][1] != 'w')
			usage();
		wordflag = 1;
		index = 2;
	}
	fp = fopen(argv[index],"rb");
	if(fp == NULL) {
		fprintf(stderr,"Couldn't open file '%s'",argv[index]);
		perror("");
		usage();
	}
	sum=0;
	mask=wordflag ? 0xffff : 0x00ff;
	while(1) {
		v = fgetc(fp);
		if(v == EOF)
			break;
		if (wordflag) {
			v <<= 8;
			c = fgetc(fp);
			if(c == EOF) {
				printf("File ended on odd byte, can't do word checksum\n");
				exit(1);
			}
			v += c;
		}
		last = v;
		sum += v;
		sum &= mask;
	}
	fclose(fp);
	if (wordflag) {
		printf("Word checksum = 0x%04x\nLast word = 0x%04x\n",sum,last);
	} else {
		printf("Byte checksum = 0x%02x\nLast byte = 0x%02x\n",sum,last);
	}
}

		
usage()
{
	printf("\nprchksum [-w] filename\n");
	printf("\nPrints checksum for file.  Does not modify file.");
	printf("\n-w flag selects word mode\n");
	exit(1);
}