tree 652c34238edcb6c558163abc3cd9d6ce7c5f91a5
parent 1527bc8b928dd1399c3d3467dd47d9ede210978a
author Borislav Petkov <borislav.petkov@amd.com> 1267806886 +0100
committer H. Peter Anvin <hpa@zytor.com> 1270594331 -0700

x86: Add optimized popcnt variants

Add support for the hardware version of the Hamming weight function,
popcnt, present in CPUs which advertize it under CPUID, Function
0x0000_0001_ECX[23]. On CPUs which don't support it, we fallback to the
default lib/hweight.c sw versions.

A synthetic benchmark comparing popcnt with __sw_hweight64 showed almost
a 3x speedup on a F10h machine.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <20100318112015.GC11152@aftab>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>