Line data    Source code

       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           0 :   MagicNumbersForDivision(T m, unsigned s, bool a)
      23        1686 :       : multiplier(m), shift(s), add(a) {}
      24           0 :   bool operator==(const MagicNumbersForDivision& rhs) const {
      25         328 :     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_