linux-kernel - Re: [PATCH 2/4] lib: vsprintf: Optimize division by 10000

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Message-ID: <CAMuHMdUt3WvLgt73L39BZ4D5_qDr7ZCYhTz6RDEsH4qV2vSa7g@mail.gmail.com>
Date:	Mon, 24 Sep 2012 17:14:00 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	George Spelvin <linux@...izon.com>
Cc:	mpn@...gle.com, vda.linux@...glemail.com, hughd@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] lib: vsprintf: Optimize division by 10000

On Mon, Sep 24, 2012 at 3:56 PM, George Spelvin <linux@...izon.com> wrote:
> Michal Nazarewicz <mpn@...gle.com> wrote:
>> Didn't some SPARCs have 32x32->32 multiply?  I remember reading some
>> rant from a GMP developer about how SPARC is broken that way.
>
> SPARCv9 only has 64x64->64; there's no 128-bit result version.
> That cuts large-integer math speed by a factor of 4 (very
> crude approximation), to the same speed as 32x32->64.
>
> SPARCv8 UMUL puts the high half of the 64-bit result into the Y
> register, and SPARCv7 has a multiply-step instruction (MULScc) which
> does likewise.

Early SPARCs don't even have a multiply instruction.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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