On Fri, 29 Jan 2010 11:04:31 +0100 Ingo Molnar <mingo@xxxxxxx> wrote: > > * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > On Fri, 29 Jan 2010 09:28:04 GMT tip-bot for Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote: > > > > > +#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)) > > > > Would be nice if it had a comment explaining why it exists. If people > > accidentally use this with non-constant arguments, the generated code > > will be pretty ghastly. > > > > Or add some barf-if-not-__constant_p() thing, perhaps. > > Yeah, agreed. > Also... Should we just do #define HWEIGHT(x) HWEIGHT64(x) and make HWEIGHT() the sole officially-exported interface? I mean, all it does is emit an obfuscated constant - perhaps we can save users from having to pick which one of the above to use by giving them a "this one always works" interface. That might require some casting to suppress "shift out of range" warnings though. <wonders if we'd otherwise end up needing an HWEIGHT_LONG()> -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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