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

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Message-ID: <20120924135614.24704.qmail@science.horizon.com>
Date:	24 Sep 2012 09:56:14 -0400
From:	"George Spelvin" <linux@...izon.com>
To:	linux@...izon.com, mpn@...gle.com, vda.linux@...glemail.com
Cc:	hughd@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] lib: vsprintf: Optimize division by 10000

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.
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