Re: Missing _BitScanReverse64()

[Pádraig Brady]

On 05/01/15 21:32, Gisle Vanem wrote:
> Pádraig Brady wrote:
> 
>> Does the following address the issue for you?
>> It should drop back to the more generic slow path on 32 bit.
> 
> But I do have _BitReverse. That could be an intrinsic.

I was assuming we could do the simpler patch and be
slightly slower on the shrinking 32 bit target.
Though I suppose it's only slightly more awkward to use
builtins where available, so I've done that in the attached.

>> BTW do we have the same issue with __popcnt64 in count-one-bits.h?
> 
> Seems so:
>    __MACHINEX64(unsigned __int64 __popcnt64(unsigned __int64))
> 
> X86 compilers only.

I've included that too, and also count-trailing-zeros is updated.

thanks,
Pádraig.

p.s. I noticed that count_one_bits() branches on the popcount_support
variable on each call, which might negate much of the gain from using this 
instruction?

gnulib-win32-64bit-intrinsics.patch
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