From owner-freebsd-hackers  Mon Jun  5 16:58:44 2000
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Date: Mon, 5 Jun 2000 16:58:38 -0700
From: Alfred Perlstein <bright@wintelcom.net>
To: "Daniel C. Sobral" <dcs@newsguy.com>
Cc: hackers@FreeBSD.ORG
Subject: Re: Optimization
Message-ID: <20000605165838.W17973@fw.wintelcom.net>
References: <200006052347.IAA00583@daniel.sobral>
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In-Reply-To: <200006052347.IAA00583@daniel.sobral>; from dcs@newsguy.com on Tue, Jun 06, 2000 at 08:47:42AM +0900
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* Daniel C. Sobral <dcs@newsguy.com> [000605 16:47] wrote:
> Can someone discuss the performance trade-offs of the following two
> alternative codes (and maybe suggest alternatives)?
> 
> Problem: I need to retrieve two values from a table.
> 
> Alternative A:
> 
> 	x = table[i].x;
> 	y = table[i].y;
> 
> Alternative B:
> 
> 	d = table[i];
> 	x = d & MASK;
> 	y = d >> SHIFT;

x = table[i];
y = x >> SHIFT;
x &= MASK;

?

I would run gcc -O3 -S on the code on several archs and see what
comes up.

-Alfred


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