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Date: Tue, 17 Feb 2015 11:12:22 -0500
From: Rich Felker <>
To: Denys Vlasenko <>
Cc: musl <>
Subject: Re: [PATCH] x86_64/memset: use "small block" code for blocks
 up to 30 bytes long

On Tue, Feb 17, 2015 at 02:08:52PM +0100, Denys Vlasenko wrote:
> >> Please see attached file.
> >
> > I tried it and it's ~1 cycle slower for at least sizes 16-30;
> > presumably we're seeing the cost of the extra compare/branch at these
> > sizes but not at others. What does your timing test show?
> See below.
> First column - result of my2.s
> Second column - result of vda1.s
> Basically, the "rep stosq" code path got a bit faster, while
> small memsets stayed the same.

Can you post your test program for me to try out? Here's what I've
been using, attached.


View attachment "memset-cycles.c" of type "text/plain" (1275 bytes)

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