Subj : Re: Multiplications faster than bit shifts?
To   : comp.programming
From : Willem
Date : Sat Jul 09 2005 08:42 pm

Eric wrote:
) I read a post by someone recently, and they asserted that multiplications by
) two were faster on recent x86 cpus than simple bit shifts. 
)
) I have a very hard time believing a simple shift would take longer than a
) multiplication and wanted to know what you people thought about this. 

A multiplication by two is (probably) slower than a shift by one bit, but
a multiplication by sixteen is probably faster than a shift by four bits.

This is because recent x86 cpus don't have barrel shifters anymore,
so they have to do X consecutive shifts to get a shift by X bits.

I'm not sure where the boundary is between a shift or a multiply
being faster.


SaSW, Willem
-- 
Disclaimer: I am in no way responsible for any of the statements
            made in the above text. For all I know I might be
            drugged or something..
            No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

.