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
34 namespace v8 {
35 namespace 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.
40 int IntegerLog2(uint32_t value);
41
42 #if defined(__GNUC__)
43
IntegerLog2(uint32_t value)44 inline int IntegerLog2(uint32_t value) {
45 return 31 - __builtin_clz(value);
46 }
47
48 #elif defined(_MSC_VER)
49
50 #pragma intrinsic(_BitScanReverse)
51
IntegerLog2(uint32_t value)52 inline 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
IntegerLog2(uint32_t value)62 inline 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