From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicolas Kaiser <nikai@nikai.net>
Subject: Re: duplicated modulo
Date: Fri, 1 Apr 2011 12:19:16 +0200
Message-ID: <20110401121916.34a567da@absol.kitzblitz>
References: <20110401114113.6e2e91af@absol.kitzblitz>
	<op.vs86ylxn3l0zgt@mnazarewicz-glaptop>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Return-path: <linux-c-programming-owner@vger.kernel.org>
In-Reply-To: <op.vs86ylxn3l0zgt@mnazarewicz-glaptop>
Sender: linux-c-programming-owner@vger.kernel.org
List-ID: <linux-c-programming.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"
To: Michal Nazarewicz <mina86@mina86.com>
Cc: linux-c-programming@vger.kernel.org

* "Michal Nazarewicz" <mina86@mina86.com>:
> On Fri, 01 Apr 2011 11:41:13 +0200, Nicolas Kaiser wrote:
> > I'm curious: a duplicated modulo operation can't possibly make
> > any difference, can it?
> >
> > diff -u -p ./arch/powerpc/platforms/powermac/nvram.c  
> > /tmp/nothing/arch/powerpc/platforms/powermac/nvram.c
> > --- ./arch/powerpc/platforms/powermac/nvram.c	2011-03-31  
> > 09:52:41.674292401 +0200
> > +++ /tmp/nothing/arch/powerpc/platforms/powermac/nvram.c
> > @@ -246,7 +246,6 @@ static u32 core99_calc_adler(u8 *buffer)
> >  	high = 0;
> >  	for (cnt=0; cnt<(NVRAM_SIZE-CORE99_ADLER_START); cnt++) {
> >  		if ((cnt % 5000) == 0) {
> > -			high  %= 65521UL;
> >  			high %= 65521UL;
> >  		}
> >  		low += buffer[cnt];
> 
> It's not just a module.  It's also an assignment.

Sure. But I fail to see where between

a %= b;
a %= b;

and

a = (a % b) % b;

and

a %= b;

would be a difference?

Best regards,
Nicolas Kaiser