Enable _BitScanForward64 at runtime

[stockfish] / src / bitcount.h

diff --git a/src/bitcount.h b/src/bitcount.h
index c6e969a82411d4b37dc1633e512ca5873d4a2912..41a1446e01b700b7d6fa08b9425b1a199a2a9122 100644 (file)
--- a/src/bitcount.h
+++ b/src/bitcount.h
@@ -66,6 +66,7 @@ inline bool cpu_has_popcnt() {
 }
 
 #define POPCNT_INTRINSIC(x) __popcnt64(x)
+#define BITSCAN_INTRINSIC(idx, x) _BitScanForward64(idx, x)
 
 #elif defined(__INTEL_COMPILER) && (defined(__x86_64) || defined(_M_X64)) // Intel compiler
 
@@ -79,12 +80,14 @@ inline bool cpu_has_popcnt() {
 }
 
 #define POPCNT_INTRINSIC(x) _mm_popcnt_u64(x)
+#define BITSCAN_INTRINSIC(idx, x) _BitScanForward64(idx, x)
 
 #else // Safe fallback for unsupported compilers
 
 inline bool cpu_has_popcnt() { return false; }
 
 #define POPCNT_INTRINSIC(x) sw_count_1s(x)
+#define BITSCAN_INTRINSIC(idx, x) sw_count_1s(x) // dummy
 
 #endif
 
@@ -183,4 +186,25 @@ const bool CpuHas64BitPath = true;
 const bool CpuHas64BitPath = false;
 #endif
 
+
+/// pop_1st_bit() finds and clears the least significant nonzero bit in a
+/// nonzero bitboard. If template parameter is true an intrinsic is called,
+/// otherwise we fallback on a software implementation.
+
+template<bool UseIntrinsic>
+inline Square pop_1st_bit(Bitboard *b) {
+
+  return pop_1st_bit(b);
+}
+
+template<>
+inline Square pop_1st_bit<true>(Bitboard *b) {
+
+  unsigned long idx;
+  Bitboard bb = *b;
+  BITSCAN_INTRINSIC(&idx, bb);
+  *b &= (bb - 1);
+  return Square(idx);
+}
+
 #endif // !defined(BITCOUNT_H_INCLUDED)