Zeljko Vrba wrote:
> I've just noticed that x86 implementations (32-bit and 64-bit) of this
> function are suboptimal: they use looping to count the bits, which is very
> slow. X86 has the dedicated BSF (bit scan forward) instruction, which
> executes in 3-4 cycles. The difference is very significant and measurable in
> certain algorithms that depend on this particular operation (e.g. van
> Emde-Boas tree).
>
> I am willing to contribute an assembly-optimized version for the x86, if
> there is any interest.
>
>
> This message posted from opensolaris.org
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Do all x86 CPUs have this instruction, or only certain families, or only
newer processors?
In any case, file a bug; I'll sponsor the request. (It would be cool to
have this both in libc and in the kernel. The kernel has both ddi_ffs
and ddi_fls.)
-- Garrett
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