Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!uwvax!oddjob!hao!noao!arizona!mike
From: mike@arizona.edu (Mike Coffin)
Newsgroups: comp.bugs.4bsd,sci.math.symbolic
Subject: Re: Bug in bc square root routine
Message-ID: <1661@megaron.arizona.edu>
Date: Mon, 27-Apr-87 15:23:15 EDT
Article-I.D.: megaron.1661
Posted: Mon Apr 27 15:23:15 1987
Date-Received: Wed, 29-Apr-87 04:41:16 EDT
References: <4534@sdcrdcf.UUCP>
Organization: U of Arizona CS Dept, Tucson
Lines: 32
Summary: The division routine is bad, too.
Xref: mnetor comp.bugs.4bsd:329 sci.math.symbolic:70

In article <4534@sdcrdcf.UUCP>, pmontgom@sdcrdcf.UUCP (Peter Montgomery)
gives an example of a bc program that produces an incorrect square root.
I do not know if this is related, but there is also bug in the division
routine of bc, at least on VAX running Berkley 4.2 and 4.3.  I had
several examples of this once; this is the only one I can find at the
moment:
-------------------------------------------------------------------------
% bc
obase=16
ibase=16
a = 519E2FEA51A537AB0132DC6F3678E8539F1BEF64109473F752
b = A2F01268A40089
a
519E2FEA51A537AB0132DC6F3678E8539F1BEF64109473F752
b
A2F01268A40089
c = a/b
c
803BF0FC7753CC1552D0A09B286CAAEBE771
a-(b*c)
F530645557A101E4C95E9095BD9
obase=A
c
11170769584511689511742018590-12440481240754033
---------------------------------------------------------------------------
The variable c in the above transcript is obviously bogus; a mod b
cannot be larger than b.  And, when printed in base 10, it contains a
minus-sign.  BTW, the correct answer for c is
803BF0FC7753CC1552D0A0CE7125CE93A4C4 (base 16).

						mike coffin
						(mike@arizona.edu)