Messages in this thread | | | Date | Wed, 03 Feb 2010 11:49:54 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 2/5] bitops: compile time optimization for hweight_long(CONSTANT) |
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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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