1 // Copyright 2006-2008 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_COMPILER_INTRINSICS_H_ 29 #define V8_COMPILER_INTRINSICS_H_ 30 31 namespace v8 { 32 namespace internal { 33 34 class CompilerIntrinsics { 35 public: 36 // Returns number of zero bits preceding least significant 1 bit. 37 // Undefined for zero value. 38 INLINE(static int CountTrailingZeros(uint32_t value)); 39 40 // Returns number of zero bits following most significant 1 bit. 41 // Undefined for zero value. 42 INLINE(static int CountLeadingZeros(uint32_t value)); 43 44 // Returns the number of bits set. 45 INLINE(static int CountSetBits(uint32_t value)); 46 }; 47 48 #ifdef __GNUC__ 49 int CompilerIntrinsics::CountTrailingZeros(uint32_t value) { 50 return __builtin_ctz(value); 51 } 52 53 int CompilerIntrinsics::CountLeadingZeros(uint32_t value) { 54 return __builtin_clz(value); 55 } 56 57 int CompilerIntrinsics::CountSetBits(uint32_t value) { 58 return __builtin_popcount(value); 59 } 60 61 #elif defined(_MSC_VER) 62 63 #pragma intrinsic(_BitScanForward) 64 #pragma intrinsic(_BitScanReverse) 65 66 int CompilerIntrinsics::CountTrailingZeros(uint32_t value) { 67 unsigned long result; //NOLINT 68 _BitScanForward(&result, static_cast<long>(value)); //NOLINT 69 return static_cast<int>(result); 70 } 71 72 int CompilerIntrinsics::CountLeadingZeros(uint32_t value) { 73 unsigned long result; //NOLINT 74 _BitScanReverse(&result, static_cast<long>(value)); //NOLINT 75 return 31 - static_cast<int>(result); 76 } 77 78 int CompilerIntrinsics::CountSetBits(uint32_t value) { 79 // Manually count set bits. 80 value = ((value >> 1) & 0x55555555) + (value & 0x55555555); 81 value = ((value >> 2) & 0x33333333) + (value & 0x33333333); 82 value = ((value >> 4) & 0x0f0f0f0f) + (value & 0x0f0f0f0f); 83 value = ((value >> 8) & 0x00ff00ff) + (value & 0x00ff00ff); 84 value = ((value >> 16) & 0x0000ffff) + (value & 0x0000ffff); 85 return value; 86 } 87 88 #else 89 #error Unsupported compiler 90 #endif 91 92 } } // namespace v8::internal 93 94 #endif // V8_COMPILER_INTRINSICS_H_ 95
