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Date: Thu, 15 Jan 2009 15:13:51 -0800
From: Maxim Sobolev <sobomax@FreeBSD.org>
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To: Christoph Mallon <christoph.mallon@gmx.de>
References: <200901142232.n0EMWhGw055895@svn.freebsd.org>	<20090115020752.52566769.stas@FreeBSD.org>	<20090114.190527.1058804377.imp@bsdimp.com>
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Cc: Alexey Dokuchaev <danfe@FreeBSD.org>, src-committers@FreeBSD.org,
	svn-src-all@FreeBSD.org, stas@FreeBSD.org, gonzo@FreeBSD.org,
	svn-src-head@FreeBSD.org, "M. Warner Losh" <imp@bsdimp.com>
Subject: Re: svn commit: r187251 - head/sys/mips/malta
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Christoph Mallon wrote:
> Alexey Dokuchaev schrieb:
>> On Wed, Jan 14, 2009 at 07:05:27PM -0700, M. Warner Losh wrote:
>>> In message: <20090115020752.52566769.stas@FreeBSD.org>
>>>             Stanislav Sedov <stas@FreeBSD.org> writes:
>>> : > +        shift = 8 * (reg & 3);
>>> : >  : : Would it make sense to replace this with
>>> : > +        shift = (reg & 3) << 3;
>>> : : to not rely on possible compiler optimizations?
>>>
>>> I don't think that it matters all that much these days...
>>
>> But the name "shift" kinda suggests << instead of *, no?
> 
> The value *is* a shift amount (see its uses a few lines down). Its name 
> does not imply the way it is calculated, but what it is used for.
> 
> BTW: Even the most cheap compilers emit shift instructions for 
> multiplication by a power of two. The new code also is clearly faster 
> then the old - quite some code gets generated for switches.

I believe Warner's point is that the code is not in the hot path, so 
that it should not really matter either way.

-Maxim