Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ryesone.UUCP
Path: utzoo!utcs!ryesone!mason
From: mason@ryesone.UUCP (Dave Mason)
Newsgroups: net.dcom,net.lan
Subject: Re: Problem with CRC calculation...need help (solved my own problem)
Message-ID: <132@ryesone.UUCP>
Date: Sun, 6-Apr-86 16:55:13 EST
Article-I.D.: ryesone.132
Posted: Sun Apr  6 16:55:13 1986
Date-Received: Mon, 7-Apr-86 11:04:22 EST
References: <130@ryesone.UUCP>
Distribution: net
Organization: Ryerson School of Computer Science, Toronto, ON
Lines: 36
Keywords: egg-on-my-face
Xref: utcs net.dcom:1778 net.lan:1380

> I thought I had a working CRC routine, but it doesn't seem to net to
> a zero.
Turns out it *was* right, but I was mangling the checksum when I put it
on the line.  The error was in my routine to validate the crc.  Basically
I divided a negative number by 256 as an attempt to shift right by 8.
> check(omsg) char *omsg; {
>     int i,j;
>     int ch;
>     char *msg;
> 	printf(">>>>>>>>\n");
> 	msg=omsg;
> 	crc=0;
> 	while (ch = *msg++)
> 		docrc(ch);
> 	docrc(0);
> 	docrc(0);
> 	i=crc/256 % 256;
<<<<<< 	i=crc>>8;
> 	j=crc %256;
> 	printf("------\n");
> 	msg=omsg;
> 	crc=0;
> 	while (ch = *msg++)
> 		docrc(ch);
> 	docrc(i);
> 	docrc(j);
> 	printf("crc=%d\n",crc);
> }
------
I wish computers were as predictable as dice!
-- 
usenet:	..!utzoo!utcsri!mason	Dave Mason, U. Toronto CSRI
	..!utzoo!ryesone!mason	Dave Mason, Ryerson Polytechnical Institute
CSNET:	mason@Toronto
ARPA:	mason%Toronto@CSNet-Relay
BITNET:	FCTY7053@RYERSON.BITNET