Message-Id:	<m0z0rEP-000S4rC@inti.gov.ar>
Comments:	Authenticated sender is <salvador AT natacha DOT inti DOT gov DOT ar>
From:	"Salvador Eduardo Tropea (SET)" <salvador AT inti DOT gov DOT ar>
Organization:	INTI
To:	EDWARD CASHIN <cashin AT pollux DOT cs DOT uga DOT edu>, djgpp AT delorie DOT com
Date:	Mon, 27 Jul 1998 14:48:24 +0000
MIME-Version:	1.0
Subject:	Re: implementation of modulo operator in djgpp
In-reply-to:	<199807271629.MAA14391@woodstock.cs.uga.edu>

EDWARD CASHIN <cashin AT pollux DOT cs DOT uga DOT edu> wrote:

> Hello.  I was just considering the case of a circular
> buffer.  Indexing the subscripts could be done with
> something like this:
> 
> /* subscripts: "front" is subscript of first stored value
> 	       "back" is subscript of last stored value
> 	       "last" is subscript of the last available 
> 			array spot */
> 
> front = (front + 1 > last) ? 0 : front + 1;
> back = (back + 1 > last) ? 0 : back + 1;
> 
> ...or you could say:
> 
> front = (++front) % last;
> back = (++back) % last;
> 
> ...which begs the question, "How fast is the modulo?"
> and more specifically, how is it implemented?

Modulo is just the rest of a division. So if last is a variable (not a macro 
and not a constant) you'll get a div or idiv and that's sllloooowwww.
But I think you must call gcc with -S to take a look at the generated 
assembler ;-)

SET 
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