From 6cfb661ca506a0d2561c9892e4a4aba523027c17 Mon Sep 17 00:00:00 2001 From: Marco Costalba Date: Sun, 25 Jan 2009 19:29:15 +0100 Subject: [PATCH] Yet another count_1s() optimization No functional change Signed-off-by: Marco Costalba --- src/bitboard.h | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/src/bitboard.h b/src/bitboard.h index 1aefd8ad..da467cd8 100644 --- a/src/bitboard.h +++ b/src/bitboard.h @@ -395,10 +395,8 @@ inline int count_1s_max_15(Bitboard b) { inline int count_1s(Bitboard b) { unsigned w = unsigned(b >> 32), v = unsigned(b); - v -= (v >> 1) & 0x55555555; // 0-2 in 2 bits - w -= (w >> 1) & 0x55555555; - v = ((v >> 2) & 0x33333333) + (v & 0x33333333); // 0-4 in 4 bits - w = ((w >> 2) & 0x33333333) + (w & 0x33333333); + v -= ((v >> 1) & 0x77777777) + ((v >> 2) & 0x33333333) + ((v & 0x88888888) >> 3); // 0-4 in 4 bits + w -= ((w >> 1) & 0x77777777) + ((w >> 2) & 0x33333333) + ((w & 0x88888888) >> 3); v = ((v >> 4) + v) & 0x0F0F0F0F; // 0-8 in 8 bits v += (((w >> 4) + w) & 0x0F0F0F0F); // 0-16 in 8 bits v *= 0x01010101; // mul is fast on amd procs @@ -407,10 +405,8 @@ inline int count_1s(Bitboard b) { inline int count_1s_max_15(Bitboard b) { unsigned w = unsigned(b >> 32), v = unsigned(b); - v -= (v >> 1) & 0x55555555; // 0-2 in 2 bits - w -= (w >> 1) & 0x55555555; - v = ((v >> 2) & 0x33333333) + (v & 0x33333333); // 0-4 in 4 bits - w = ((w >> 2) & 0x33333333) + (w & 0x33333333); + v -= ((v >> 1) & 0x77777777) + ((v >> 2) & 0x33333333) + ((v & 0x88888888) >> 3); // 0-4 in 4 bits + w -= ((w >> 1) & 0x77777777) + ((w >> 2) & 0x33333333) + ((w & 0x88888888) >> 3); v += w; // 0-8 in 4 bits v *= 0x11111111; return int(v >> 28); -- 2.39.2