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 24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 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 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 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 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