Fix implementation of bit count functions.

src/base/bits.h

Index: src/base/bits.h
diff --git a/src/base/bits.h b/src/base/bits.h
index ec0f5517a9d34d5ae593432749199b5ab9ec308f..129bf6268c677ae0a562630565508e24f54853a3 100644
--- a/src/base/bits.h
+++ b/src/base/bits.h
@@ -6,6 +6,9 @@
 #define V8_BASE_BITS_H_
 
 #include "include/v8stdint.h"
+#if V8_CC_MSVC
+#include <intrin.h>
+#endif
 #if V8_OS_WIN32
 #include "src/base/win32-headers.h"
 #endif
@@ -14,6 +17,61 @@ namespace v8 {
 namespace base {
 namespace bits {
 
+// CountSetBits32(value) returns the number of bits set in |value|.
+inline uint32_t CountSetBits32(uint32_t value) {
+#if V8_HAS_BUILTIN_POPCOUNT
+  return __builtin_popcount(value);
+#else
+  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
+}
+
+
+// CountLeadingZeros32(value) returns the number of zero bits following the most
+// significant 1 bit in |value| if |value| is non-zero, otherwise it returns 32.
+inline uint32_t CountLeadingZeros32(uint32_t value) {
+#if V8_HAS_BUILTIN_CLZ
+  return value ? __builtin_clz(value) : 32;
+#elif V8_CC_MSVC
+  unsigned long result;  // NOLINT(runtime/int)
+  if (!_BitScanReverse(&result, value)) return 32;
+  return static_cast<uint32_t>(31 - result);
+#else
+  value = value | (value >> 1);
+  value = value | (value >> 2);
+  value = value | (value >> 4);
+  value = value | (value >> 8);
+  value = value | (value >> 16);
+  return CountSetBits32(~value);
+#endif
+}
+
+
+// CountTrailingZeros32(value) returns the number of zero bits preceding the
+// least significant 1 bit in |value| if |value| is non-zero, otherwise it
+// returns 32.
+inline uint32_t CountTrailingZeros32(uint32_t value) {
+#if V8_HAS_BUILTIN_CTZ
+  return value ? __builtin_ctz(value) : 32;
+#elif V8_CC_MSVC
+  unsigned long result;  // NOLINT(runtime/int)
+  if (!_BitScanForward(&result, value)) return 32;
+  return static_cast<uint32_t>(result);
+#else
+  if (value == 0) return 32;
+  unsigned count = 0;
+  for (value ^= value - 1; value >>= 1; ++count)
+    ;
+  return count;
+#endif
+}
+
+
 inline uint32_t RotateRight32(uint32_t value, uint32_t shift) {
   if (shift == 0) return value;
   return (value >> shift) | (value << (32 - shift));