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From: Rich Felker <dalias@libc.org>
To: Denys Vlasenko <vda.linux@googlemail.com>
Cc: musl <musl@lists.openwall.com>
Subject: Re: [PATCH] x86_64/memset: use "small block" code for blocks up to 30 bytes long
Date: Mon, 16 Feb 2015 10:12:49 -0500	[thread overview]
Message-ID: <20150216151249.GX23507@brightrain.aerifal.cx> (raw)
In-Reply-To: <CAK1hOcNRpkN_cK_sfW396+c41iops4weO_jVu2JEb7rs2h2JyQ@mail.gmail.com>

On Mon, Feb 16, 2015 at 11:09:25AM +0100, Denys Vlasenko wrote:
> On Sun, Feb 15, 2015 at 11:55 PM, Rich Felker <dalias@libc.org> wrote:
> >> "sub $8,%rcx" can be folded into lea.
> >
> > No, it can't, for the above reason.
> 
> Why can't?
> 
> lea -9(%rdx), %rcx
> 
> will also underflow for %rdx == 0, just like "lea -1".

Then n==1..8 would also fall into the rep stosq path and either fail
horribly or need to use slow fixup code there.

Rich


  reply	other threads:[~2015-02-16 15:12 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-13 16:39 Denys Vlasenko
2015-02-14 19:35 ` Rich Felker
2015-02-15  4:06   ` Rich Felker
2015-02-15 14:07     ` Denys Vlasenko
2015-02-15 15:03       ` Rich Felker
2015-02-15 21:44         ` Denys Vlasenko
2015-02-15 22:55           ` Rich Felker
2015-02-16 10:09             ` Denys Vlasenko
2015-02-16 15:12               ` Rich Felker [this message]
2015-02-16 17:36           ` Rich Felker
2015-02-17 13:08             ` Denys Vlasenko
2015-02-17 16:12               ` Rich Felker
2015-02-17 16:51                 ` Denys Vlasenko
2015-02-17 17:30                   ` Denys Vlasenko
2015-02-17 17:40                   ` Rich Felker
2015-02-17 18:53                     ` Denys Vlasenko
2015-02-17 21:12                       ` Rich Felker
2015-02-18  9:05                         ` Denys Vlasenko

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