1// Copyright 2011 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef V8_MISC_INTRINSICS_H_
6#define V8_MISC_INTRINSICS_H_
7
8#include "include/v8.h"
9#include "src/globals.h"
10
11namespace v8 {
12namespace internal {
13
14// Returns the index of the leading 1 bit, counting the least significant bit at
15// index 0.  (1 << IntegerLog2(x)) is a mask for the most significant bit of x.
16// Result is undefined if input is zero.
17int IntegerLog2(uint32_t value);
18
19#if defined(__GNUC__)
20
21inline int IntegerLog2(uint32_t value) {
22  return 31 - __builtin_clz(value);
23}
24
25#elif defined(_MSC_VER)
26
27#pragma intrinsic(_BitScanReverse)
28
29inline int IntegerLog2(uint32_t value) {
30  unsigned long result;             // NOLINT: MSVC intrinsic demands this type.
31  _BitScanReverse(&result, value);
32  return result;
33}
34
35#else
36
37// Default version using regular operations. Code taken from:
38// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
39inline int IntegerLog2(uint32_t value) {
40  int result, shift;
41
42  shift = (value > 0xFFFF) << 4;
43  value >>= shift;
44  result = shift;
45
46  shift = (value > 0xFF) << 3;
47  value >>= shift;
48  result |= shift;
49
50  shift = (value > 0xF) << 2;
51  value >>= shift;
52  result |= shift;
53
54  shift = (value > 0x3) << 1;
55  value >>= shift;
56  result |= shift;
57
58  result |= (value >> 1);
59
60  return result;
61}
62#endif
63
64} }  // namespace v8::internal
65
66#endif  // V8_MISC_INTRINSICS_H_
67