[v8-dev] Optimise Math.floor(x/y) to use integer division for specific divisor....

src/compiler-intrinsics.h

Index: src/compiler-intrinsics.h
===================================================================
--- src/compiler-intrinsics.h	(revision 11426)
+++ src/compiler-intrinsics.h	(working copy)
@@ -40,6 +40,9 @@
   // Returns number of zero bits following most significant 1 bit.
   // Undefined for zero value.
   INLINE(static int CountLeadingZeros(uint32_t value));
+
+  // Returns the number of bits set.
+  INLINE(static int CountSetBits(uint32_t value));
 };
 
 #ifdef __GNUC__
@@ -51,6 +54,10 @@
   return __builtin_clz(value);
 }
 
+int CompilerIntrinsics::CountSetBits(uint32_t value) {
+  return __builtin_popcount(value);
+}
+
 #elif defined(_MSC_VER)
 
 #pragma intrinsic(_BitScanForward)
@@ -68,7 +75,24 @@
   return 31 - static_cast<int>(result);
 }
 
+int CompilerIntrinsics::CountSetBits(uint32_t value) {
+  // __popcnt is only supported from VS2008.
+#define _MSC_VER_VS2008 1500
+#if _MSC_VER >= _MSC_VER_VS2008
+  return __popcnt(value);
 #else
+  // Manually count set bits.
+  value = ((value >>  1) & 0x55555555) + (value & 0x55555555);
+  value = ((value >>  2) & 0x33333333) + (value & 0x33333333);
+  value = ((value >>  4) & 0x0f0f0f0f) + (value & 0x0f0f0f0f);
+  value = ((value >>  8) & 0x00ff00ff) + (value & 0x00ff00ff);
+  value = ((value >> 16) & 0x0000ffff) + (value & 0x0000ffff);
+  return value;
+#endif
+#undef _MSC_VER_VS2008
+}
+
+#else
 #error Unsupported compiler
 #endif