Messages in this thread |  | | | Date | Fri, 29 Jan 2010 11:32:00 +0100 | | Subject | Re: [PATCH 07/10] bitops: Provide compile time HWEIGHT{8,16,32,64} | | From | John Kacur <> |
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On Fri, Jan 22, 2010 at 4:50 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > Provide compile time versions of hweight. > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > LKML-Reference: <new-submission> > --- > include/linux/bitops.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > Index: linux-2.6/include/linux/bitops.h > =================================================================== > --- linux-2.6.orig/include/linux/bitops.h > +++ linux-2.6/include/linux/bitops.h > @@ -45,6 +45,20 @@ static inline unsigned long hweight_long > return sizeof(w) == 4 ? hweight32(w) : hweight64(w); > }
I like it. Maybe provide a comment that this provides the Hamming weight, it took me a second to realize what this was.
> > +#define HWEIGHT8(w) \ > + ( (!!((w) & (1ULL << 0))) + \ > + (!!((w) & (1ULL << 1))) + \ > + (!!((w) & (1ULL << 2))) + \ > + (!!((w) & (1ULL << 3))) + \ > + (!!((w) & (1ULL << 4))) + \ > + (!!((w) & (1ULL << 5))) + \ > + (!!((w) & (1ULL << 6))) + \ > + (!!((w) & (1ULL << 7))) ) > + > +#define HWEIGHT16(w) (HWEIGHT8(w) + HWEIGHT8(w >> 8)) > +#define HWEIGHT32(w) (HWEIGHT16(w) + HWEIGHT16(w >> 16)) > +#define HWEIGHT64(w) (HWEIGHT32(w) + HWEIGHT32(w >> 32)) > + > /** > * rol32 - rotate a 32-bit value left > * @word: value to rotate > > -- > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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