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From: chris@mimsy.UUCP
Newsgroups: comp.sys.m68k
Subject: Re: Incidentally ...
Message-ID: <6139@mimsy.UUCP>
Date: Sat, 4-Apr-87 20:04:56 EST
Article-I.D.: mimsy.6139
Posted: Sat Apr  4 20:04:56 1987
Date-Received: Sun, 5-Apr-87 14:27:48 EST
References: <362@sbcs.UUCP> <1466@ncr-sd.SanDiego.NCR.COM> <580@plx.UUCP> <6134@mimsy.UUCP>
Distribution: comp
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 21

In article <6134@mimsy.UUCP> I wrote:
>[use] while (--j >= 0) [rather than while (j--)]

I poked around today and discovered that Sun's compiler, at least,
will turn

	register short j;	/* but not `register int j' */

	while (--j != -1)
		...

into a `dbra' loop.  If you are willing to put machine dependent
source optimisations into your C code, this might be something to
consider (at least for inner loops).

Anyway, it is a good idea to profile, tune, compile to assembly
code, and sometimes even hand-tweak the results, in speed-critical
routines.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	seismo!mimsy!chris	ARPA/CSNet:	chris@mimsy.umd.edu