On Mon, Mar 28, 2016 at 11:29:15AM -0400, David Miller wrote: > From: Zeng Zhaoxiu <zhaoxiu.zeng@xxxxxxxxx> > Date: Mon, 28 Mar 2016 13:44:03 +0800 > > > 在 2016年03月28日 10:43, David Miller 写道: > >> From: "zhaoxiu.zeng" <zhaoxiu.zeng@xxxxxxxxx> > >> Date: Sun, 27 Mar 2016 14:43:10 +0800 > >> > >>> + > >>> +/* > >>> + * parityN: returns the parity of a N-bit word, > >>> + * i.e. the number of 1-bits in x modulo 2. > >>> + */ > >>> + > >>> +#define __arch_parity4(w) (__arch_hweight8((w) & 0xf) & 1) > >>> +#define __arch_parity8(w) (__arch_hweight8(w) & 1) > >>> +#define __arch_parity16(w) (__arch_hweight16(w) & 1) > >>> +#define __arch_parity32(w) (__arch_hweight32(w) & 1) > >>> +#define __arch_parity64(w) ((unsigned int)__arch_hweight64(w) & 1) > >> This looks like asm-generic/ material to me. > > > > This is generic for the architectures which have popcount instruction, > > but more higher costs than asm-generic/ for others. > > Which is why said stanza's in the asm-generic header should be triggered > by a CPP define or similar. For sparc we would need to do a run-time patch as far as I see. If popc is availble then use of hweight* should be fine. But without popc then I think the generic implementation that uses the stanford algorithm would be most efficient, rather than the base this on the generic hweight functions. Sam -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
