linux-kernel - Re: [PATCH 1/4] lib: vsprintf: Optimize division by 10 for small integers.

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Message-ID: <20120924141805.28256.qmail@science.horizon.com>
Date:	24 Sep 2012 10:18:05 -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 1/4] lib: vsprintf: Optimize division by 10 for small integers.

Michal Nazarewicz <mpn@...gle.com> wrote:
> On Fri, Aug 03 2012, George Spelvin <linux@...izon.com> wrote:
>> Shrink the reciprocal approximations used in put_dec_full4
>> based on the comments in put_dec_full9.
>
> Have you verified that the comment is correct?

I rechecked all the validity limits myself.

>>  	r      = (q * 0xcd) >> 11;

> If you are changing everything, this could also be changed to:
>
>	r      = (q * 0x67) >> 10;
>
> no?

Also in those comments is a statement I did *not* recheck, as it didn't
affect correctness, saying that 0xcd produces shorter code than 0x67 on
x86 (if the code is generated using shifts and adds).

That's why I left it that way.
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