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
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.
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13 // contributors may be used to endorse or promote products derived
14 // from this software without specific prior written permission.
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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28 #ifndef V8_MISC_INTRINSICS_H_
29 #define V8_MISC_INTRINSICS_H_
31 #include "../include/v8.h"
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);
44 inline int IntegerLog2(uint32_t value) {
45 return 31 - __builtin_clz(value);
48 #elif defined(_MSC_VER)
50 #pragma intrinsic(_BitScanReverse)
52 inline int IntegerLog2(uint32_t value) {
53 unsigned long result; // NOLINT: MSVC intrinsic demands this type.
54 _BitScanReverse(&result, value);
60 // Default version using regular operations. Code taken from:
61 // http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
62 inline int IntegerLog2(uint32_t value) {
65 shift = (value > 0xFFFF) << 4;
69 shift = (value > 0xFF) << 3;
73 shift = (value > 0xF) << 2;
77 shift = (value > 0x3) << 1;
81 result |= (value >> 1);
87 } } // namespace v8::internal
89 #endif // V8_MISC_INTRINSICS_H_