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Yet another count_1s() optimization

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No functional change

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-01-25 19:29:15 +01:00
parent be43219136
commit 6cfb661ca5
1 changed files with 4 additions and 8 deletions
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12
src/bitboard.h
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@ -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);