Macintoshes. Some of the bitboard routines in the current version of\r
Stockfish are endianness-sensitive, and won't work on a big-endian CPU.\r
\r
+Stockfish has POPCNT instruction runtime detection and support. This can\r
+give an extra speed on Core i7 or similar systems. To enable this feature\r
+(disabled by default) simply uncomment #define USE_POPCNT in bitcount.h\r
+before to compile.\r
+\r
+On 64 bit Unix-like systems the 'bsfq' assembly instruction will be used\r
+for bit counting. Detection is automatic at compile time, but in case you\r
+experience compile problems you can comment out #define USE_BSFQ line in types.h\r
+\r
\r
5. Terms of use\r
---------------\r
#if !defined(BITCOUNT_H_INCLUDED)
#define BITCOUNT_H_INCLUDED
-// To disable POPCNT support uncomment NO_POPCNT define. You should do it only
-// in PGO compiling to exercise the default fallback path. Don't forget to
-// re-comment the line for the final optimized compile though ;-)
+// To enable POPCNT support uncomment USE_POPCNT define. For PGO compile on a Core i7
+// you may want to collect profile data first with USE_POPCNT disabled and then, in a
+// second profiling session, with USE_POPCNT enabled so to exercise both paths. Don't
+// forget to leave USE_POPCNT enabled for the final optimized compile though ;-)
-//#define NO_POPCNT
+//#define USE_POPCNT
#include "types.h"
// Select type of intrinsic bit count instruction to use
-#if defined(_MSC_VER) && defined(IS_64BIT) && !defined(NO_POPCNT) // Microsoft compiler
+#if defined(_MSC_VER) && defined(IS_64BIT) && defined(USE_POPCNT) // Microsoft compiler
#include <intrin.h>
#define POPCNT_INTRINSIC(x) __popcnt64(x)
-#elif defined(__INTEL_COMPILER) && defined(IS_64BIT) && !defined(NO_POPCNT) // Intel compiler
+#elif defined(__INTEL_COMPILER) && defined(IS_64BIT) && defined(USE_POPCNT) // Intel compiler
#include <nmmintrin.h>
#define POPCNT_INTRINSIC(x) _mm_popcnt_u64(x)
-#else // Safe fallback for unsupported compilers or when NO_POPCNT is defined
+#else // Safe fallback for unsupported compilers or when USE_POPCNT is disabled
inline bool cpu_has_popcnt() { return false; }
// Global constant initialized at startup that is set to true if
// CPU on which application runs supports POPCNT intrinsic. Unless
-// NO_POPCNT is defined.
-#if defined(NO_POPCNT)
-const bool CpuHasPOPCNT = false;
-#else
+// USE_POPCNT is not defined.
const bool CpuHasPOPCNT = cpu_has_popcnt();
-#endif
// Global constant used to print info about the use of 64 optimized