Message-ID: <414A7A01.9080708@nortelnetworks.com>
Date: Thu, 16 Sep 2004 23:45:37 -0600
From: Chris Friesen <cfriesen@nortelnetworks.com>
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CC: Andrew Morton <akpm@osdl.org>, Stelian Pop <stelian@popies.net>,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC, 2.6] a simple FIFO implementation
References: <16714.14118.212946.499226@wombat.chubb.wattle.id.au>
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Peter Chubb wrote:

> This depends on how expensive % is.  On IA64, something like this:
> 
>      add(char c) {
> 	     int i = p->head == p->len ? p->head++ : 0;
> 	     p->buf[i] = c;
>      }
> 
> is cheaper, as % generates a subroutine call to __modsi3.  It also is
> shorter =-- 12 bundles as opposed to 15.

I did a similar test once for ppc that found that an increment followed by a 
test (marked unlikely) was actually quicker in practice than modulo arithmetic. 
  The branch predictor got it right most of the time, so the test was almost free.

Chris
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