Re: [PATCH] Remove some divide instructions

[Linus Torvalds]

On Wed, 27 Oct 2004, Zachary Amsden wrote:
>
> I noticed several 64-bit divides for HZ/USER_HZ, and also the fact that 
> HZ == USER_HZ on many architectures (or if you play with scaling it ;).  
> Since do_div is macroized to optimized assembler on many platforms, we 
> emit long divides for divide by one.  This could be extended further to 
> recognize other power of two divides, but I don't think the complexity 
> of the macros would be justified.  I also didn't feel it was worthwhile 
> to optimize this for non-constant divides; if you feel otherwise, please 
> extend.

Can you test out the trivial extension, which is to allow any power-of-two
constant, and just leave it as a divide in those cases (and let the
compiler turn it into a 64-bit shift)?

It's very easy to test for powers of two: !((x) & ((x)-1)) does it for 
everything but zero, and zero in this case is an error anyway.

		Linus
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