From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 11 Jan 2009 16:15:18 +0000 (+0100)
Subject: Rewrite count_1s() to be similar to 64bit counterpart
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=3e6e57231ecb1c23e43e02109efa3bcaf7ebe7c3;hp=14c1fd4d27fa3bf9b4b68ffe3b088160ba6cbee4

Rewrite count_1s() to be similar to 64bit counterpart

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---

diff --git a/src/bitboard.h b/src/bitboard.h
index 11406648..2280f66c 100644
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -395,23 +395,23 @@ inline int count_1s_max_15(Bitboard b) {
 
 inline int count_1s(Bitboard b) {
   unsigned w = unsigned(b >> 32), v = unsigned(b);
-  v = v - ((v >> 1) & 0x55555555);
-  w = w - ((w >> 1) & 0x55555555);
+  v -= (v >> 1) & 0x55555555;
+  w -= (w >> 1) & 0x55555555;
   v += w;
-  v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
-  v = (v + (v >> 4)) & 0x0F0F0F0F;
-  v = (v * 0x01010101) >> 24; // mul is fast on amd procs
-  return int(v);
+  v = ((v >> 2) & 0x33333333) + (v & 0x33333333);
+  v = ((v >> 4) + v) & 0x0F0F0F0F;
+  v *= 0x01010101; // mul is fast on amd procs
+  return int(v >> 24);
 }
 
 inline int count_1s_max_15(Bitboard b) {
   unsigned w = unsigned(b >> 32), v = unsigned(b);
-  v = v - ((v >> 1) & 0x55555555);
-  w = w - ((w >> 1) & 0x55555555);
+  v -= (v >> 1) & 0x55555555;
+  w -= (w >> 1) & 0x55555555;
   v += w;
-  v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
-  v = (v * 0x11111111) >> 28;
-  return int(v);
+  v = ((v >> 2) & 0x33333333) + (v & 0x33333333);
+  v *= 0x11111111;
+  return int(v >> 28);
 }
 
 #elif defined(BITCOUNT_SWAR_64)