1// Copyright 2011 the V8 project authors. All rights reserved.
2// Redistribution and use in source and binary forms, with or without
3// modification, are permitted provided that the following conditions are
4// met:
5//
6//     * Redistributions of source code must retain the above copyright
7//       notice, this list of conditions and the following disclaimer.
8//     * Redistributions in binary form must reproduce the above
9//       copyright notice, this list of conditions and the following
10//       disclaimer in the documentation and/or other materials provided
11//       with the distribution.
12//     * Neither the name of Google Inc. nor the names of its
13//       contributors may be used to endorse or promote products derived
14//       from this software without specific prior written permission.
15//
16// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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25// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27
28#ifndef V8_MISC_INTRINSICS_H_
29#define V8_MISC_INTRINSICS_H_
30
31#include "../include/v8.h"
32#include "globals.h"
33
34namespace v8 {
35namespace internal {
36
37// Returns the index of the leading 1 bit, counting the least significant bit at
38// index 0.  (1 << IntegerLog2(x)) is a mask for the most significant bit of x.
39// Result is undefined if input is zero.
40int IntegerLog2(uint32_t value);
41
42#if defined(__GNUC__)
43
44inline int IntegerLog2(uint32_t value) {
45  return 31 - __builtin_clz(value);
46}
47
48#elif defined(_MSC_VER)
49
50#pragma intrinsic(_BitScanReverse)
51
52inline int IntegerLog2(uint32_t value) {
53  unsigned long result;             // NOLINT: MSVC intrinsic demands this type.
54  _BitScanReverse(&result, value);
55  return result;
56}
57
58#else
59
60// Default version using regular operations. Code taken from:
61// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
62inline int IntegerLog2(uint32_t value) {
63  int result, shift;
64
65  shift = (value > 0xFFFF) << 4;
66  value >>= shift;
67  result = shift;
68
69  shift = (value > 0xFF) << 3;
70  value >>= shift;
71  result |= shift;
72
73  shift = (value > 0xF) << 2;
74  value >>= shift;
75  result |= shift;
76
77  shift = (value > 0x3) << 1;
78  value >>= shift;
79  result |= shift;
80
81  result |= (value >> 1);
82
83  return result;
84}
85#endif
86
87} }  // namespace v8::internal
88
89#endif  // V8_MISC_INTRINSICS_H_
90