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Path: utzoo!watmath!watcgl!dmmartindale
From: dmmartindale@watcgl.UUCP (Dave Martindale)
Newsgroups: net.bugs.4bsd
Subject: Re: (more) missed optimizations in pcc
Message-ID: <515@watcgl.UUCP>
Date: Wed, 21-Nov-84 00:04:34 EST
Article-I.D.: watcgl.515
Posted: Wed Nov 21 00:04:34 1984
Date-Received: Wed, 21-Nov-84 01:40:43 EST
References: <1214@umcp-cs.UUCP>
Distribution: net
Organization: U of Waterloo, Ontario
Lines: 13

> Index: lib/pcc/local.c 4.2 Fix
> 
> Description:
> 	The machine dependent expression optimizer doesn't handle
> 	"%" or "%=" by the constants which are powers of two.  These
> 	can be done more simply as "&" or "&=".

But "fixing" this gives you an answer that is different from what you
would have gotten had you done the divide/multiply/subtract in cases
where the "dividend" is negative.  For example, if the variable "i"
contains the value -7 and "j" contains "4", then i%j is -3 while
i%4 is 1 (with your optimization).  Are you sure you want to introduce
an inconsistency like this?  I don't like it.