On Sun, Feb 13, 2011 at 02:11:30PM -0800, Matt Thomas wrote: > > On Feb 13, 2011, at 12:10 PM, Joerg Sonnenberger wrote: > > > On Sun, Feb 13, 2011 at 10:44:45AM -0800, Matt Thomas wrote: > >> CountBitsInByte should be replaced by __builtin_popcount so that > >> machines with a popcount instruction can use it. > > > > Which ones? There is no assembler version of popcount at the moment. > > SPARC64 doesn't use it for ffs(), the AMD64 one has to be detected via > > CPUID. The libgcc version is pretty bad. But code can use the popcount > > family... > > popcnt != clz
I didn't say they are the same. But clz can be implemented using popcount. > alpha ev6 > i386 has a sse2 popcnt > power5 has a popcntb > > sparcv9 has one but none of the UltraSparc implement it. > > Also, use a count-leading instruction might be useful with > a faster popcount. There is no implementation in src/common for either of this. I have the code for i386/amd64 on my disk, but it would require adding another library for little gain. Joerg
