Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!tank!mimsy!chris
From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.graphics
Subject: Re: Integral Square Root
Message-ID: <21550@mimsy.umd.edu>
Date: 30 Dec 89 20:42:23 GMT
References: <9170@cbmvax.commodore.com>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 18

In article <9170@cbmvax.commodore.com> mitchell@cbmvax.commodore.com
(Fred Mitchell - PA) writes:
>Here's one that is short, fast, and sweet.

... and wrong: the line

       if ( (rb = r+(b=1<<i)) * rb <= n)

uses and sets rb in an unknown order.  (Mr. Mitchell's compiler clearly
does the assignment, then the evaluation of the second `rb', then the
multiplication, but a compiler is free to evaluate the second `rb', then
compute r+..., assign that to rb, multiply that by the old value of rb,
and compare with n.)  The simplest fix is to break up the three embedded
statements (b=, rb=, if...), which also leads to more easily understood
code.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@cs.umd.edu	Path:	uunet!mimsy!chris