Re: [PATCH 2/5] bitops: compile time optimization for hweight_long(CONSTANT)

[H. Peter Anvin]

On 02/03/2010 10:47 AM, Peter Zijlstra wrote:
> On Wed, 2010-02-03 at 19:14 +0100, Borislav Petkov wrote:
> 
>> alternative("call hweightXX", "popcnt", X86_FEATURE_POPCNT)
> 
> Make sure to apply a 0xff bitmask to the popcnt r16 call for hweight8(),
> and hweight64() needs a bit of magic for 32bit, but yes, something like
> that ought to work nicely.
> 

Arguably the "best" option is to have the alternative being a jump to an
out-of-line stub which does the necessary parameter marshalling before
calling a stub.  This technique is already used in a few other places.

	-hpa
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