1 // Copyright 2014 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef V8_BASE_DIVISION_BY_CONSTANT_H_ 6 #define V8_BASE_DIVISION_BY_CONSTANT_H_ 7 8 #include <stdint.h> 9 10 #include "src/base/base-export.h" 11 12 namespace v8 { 13 namespace base { 14 15 // ---------------------------------------------------------------------------- 16 17 // The magic numbers for division via multiplication, see Warren's "Hacker's 18 // Delight", chapter 10. The template parameter must be one of the unsigned 19 // integral types. 20 template <class T> 21 struct V8_BASE_EXPORT MagicNumbersForDivision { 22 MagicNumbersForDivision(T m, unsigned s, bool a) 23 : multiplier(m), shift(s), add(a) {} 24 bool operator==(const MagicNumbersForDivision& rhs) const { 25 return multiplier == rhs.multiplier && shift == rhs.shift && add == rhs.add; 26 } 27 28 T multiplier; 29 unsigned shift; 30 bool add; 31 }; 32 33 34 // Calculate the multiplier and shift for signed division via multiplication. 35 // The divisor must not be -1, 0 or 1 when interpreted as a signed value. 36 template <class T> 37 V8_BASE_EXPORT MagicNumbersForDivision<T> SignedDivisionByConstant(T d); 38 39 // Calculate the multiplier and shift for unsigned division via multiplication, 40 // see Warren's "Hacker's Delight", chapter 10. The divisor must not be 0 and 41 // leading_zeros can be used to speed up the calculation if the given number of 42 // upper bits of the dividend value are known to be zero. 43 template <class T> 44 V8_BASE_EXPORT MagicNumbersForDivision<T> UnsignedDivisionByConstant( 45 T d, unsigned leading_zeros = 0); 46 47 extern template V8_BASE_EXPORT MagicNumbersForDivision<uint32_t> 48 SignedDivisionByConstant(uint32_t d); 49 extern template V8_BASE_EXPORT MagicNumbersForDivision<uint64_t> 50 SignedDivisionByConstant(uint64_t d); 51 52 extern template V8_BASE_EXPORT MagicNumbersForDivision<uint32_t> 53 UnsignedDivisionByConstant(uint32_t d, unsigned leading_zeros); 54 extern template V8_BASE_EXPORT MagicNumbersForDivision<uint64_t> 55 UnsignedDivisionByConstant(uint64_t d, unsigned leading_zeros); 56 57 } // namespace base 58 } // namespace v8 59 60 #endif // V8_BASE_DIVISION_BY_CONSTANT_H_ 61
