Fix implementation of bit count functions.

src/compiler-intrinsics.h

-// Copyright 2006-2008 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef V8_COMPILER_INTRINSICS_H_
-#define V8_COMPILER_INTRINSICS_H_
-
-#include "src/base/macros.h"
-
-namespace v8 {
-namespace internal {
-
-class CompilerIntrinsics {
- public:
-  // Returns number of zero bits preceding least significant 1 bit.
-  // Undefined for zero value.
-  INLINE(static int CountTrailingZeros(uint32_t value));
-
-  // 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__
-int CompilerIntrinsics::CountTrailingZeros(uint32_t value) {
-  return __builtin_ctz(value);
-}
-
-int CompilerIntrinsics::CountLeadingZeros(uint32_t value) {
-  return __builtin_clz(value);
-}
-
-int CompilerIntrinsics::CountSetBits(uint32_t value) {
-  return __builtin_popcount(value);
-}
-
-#elif defined(_MSC_VER)
-
-#pragma intrinsic(_BitScanForward)
-#pragma intrinsic(_BitScanReverse)
-
-int CompilerIntrinsics::CountTrailingZeros(uint32_t value) {
-  unsigned long result;  //NOLINT
-  _BitScanForward(&result, static_cast<long>(value));  //NOLINT
-  return static_cast<int>(result);
-}
-
-int CompilerIntrinsics::CountLeadingZeros(uint32_t value) {
-  unsigned long result;  //NOLINT
-  _BitScanReverse(&result, static_cast<long>(value));  //NOLINT
-  return 31 - static_cast<int>(result);
-}
-
-int CompilerIntrinsics::CountSetBits(uint32_t value) {
-  // 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;
-}
-
-#else
-#error Unsupported compiler
-#endif
-
-} }  // namespace v8::internal
-
-#endif  // V8_COMPILER_INTRINSICS_H_