From: Marco Costalba <mcostalba@gmail.com>
Date: Thu, 17 Mar 2011 12:47:15 +0000 (+0100)
Subject: Use intrinsic in pop_1st_bit() under MSVC 64 bits
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=5ea08e79c4e510b65b3e18c9ab09919132976eec;ds=sidebyside

Use intrinsic in pop_1st_bit() under MSVC 64 bits

Around 1% speedup when compiled with MSVC 64

No functional change.

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

diff --git a/src/bitboard.h b/src/bitboard.h
index 2451c139..97048394 100644
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -257,15 +257,25 @@ inline bool squares_aligned(Square s1, Square s2, Square s3) {
 /// pop_1st_bit() finds and clears the least significant nonzero bit in a
 /// nonzero bitboard.
 
-#if defined(USE_BSFQ) // Assembly code by Heinz van Saanen
+#if defined(USE_BSFQ)
 
-inline Square first_1(Bitboard b) {
+#if defined(_MSC_VER) && !defined(__INTEL_COMPILER)
+
+FORCE_INLINE Square first_1(Bitboard b) {
+   unsigned long index;
+   _BitScanForward64(&index, b);
+   return (Square) index;
+}
+#else
+
+FORCE_INLINE Square first_1(Bitboard b) { // Assembly code by Heinz van Saanen
   Bitboard dummy;
   __asm__("bsfq %1, %0": "=r"(dummy): "rm"(b) );
-  return (Square)(dummy);
+  return (Square) dummy;
 }
+#endif
 
-inline Square pop_1st_bit(Bitboard* b) {
+FORCE_INLINE Square pop_1st_bit(Bitboard* b) {
   const Square s = first_1(*b);
   *b &= ~(1ULL<<s);
   return s;
diff --git a/src/types.h b/src/types.h
index a5502c2f..623e51d9 100644
--- a/src/types.h
+++ b/src/types.h
@@ -77,9 +77,8 @@ typedef unsigned __int64 uint64_t;
 #define IS_64BIT
 #endif
 
-// Automatic detection for use of bsfq asm-instruction under Windows.
-// Works only in 64-bit mode. Does not work with MSVC.
-#if defined(_WIN64) && defined(__INTEL_COMPILER)
+// Automatic detection for use of bsfq asm-instruction under Windows
+#if defined(_WIN64)
 #define USE_BSFQ
 #endif