svn commit: r187251 - head/sys/mips/malta

Christoph Mallon christoph.mallon at gmx.de
Thu Jan 15 03:58:20 PST 2009


Alexey Dokuchaev schrieb:
> On Wed, Jan 14, 2009 at 07:05:27PM -0700, M. Warner Losh wrote:
>> In message: <20090115020752.52566769.stas at FreeBSD.org>
>>             Stanislav Sedov <stas at 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.


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