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 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