chromium/v8/src/base/division-by-constant.h

// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_BASE_DIVISION_BY_CONSTANT_H_
#define V8_BASE_DIVISION_BY_CONSTANT_H_

#include <stdint.h>

#include <tuple>
#include <type_traits>

#include "src/base/base-export.h"
#include "src/base/export-template.h"

namespace v8 {
namespace base {

// ----------------------------------------------------------------------------

// The magic numbers for division via multiplication, see Warren's "Hacker's
// Delight", chapter 10.
template <class T>
struct EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT) MagicNumbersForDivision { … };

// Calculate the multiplier and shift for signed division via multiplication.
// The divisor must not be -1, 0 or 1 when interpreted as a signed value.
template <class T, std::enable_if_t<std::is_unsigned_v<T>, bool> = true>
EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT)
MagicNumbersForDivision<T> SignedDivisionByConstant(T d);

template <class T, std::enable_if_t<std::is_signed_v<T>, bool> = true>
MagicNumbersForDivision<T> SignedDivisionByConstant(T d) { … }

// Calculate the multiplier and shift for unsigned division via multiplication,
// see Warren's "Hacker's Delight", chapter 10. The divisor must not be 0 and
// leading_zeros can be used to speed up the calculation if the given number of
// upper bits of the dividend value are known to be zero.
template <class T>
EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT)
MagicNumbersForDivision<T> UnsignedDivisionByConstant(
    T d, unsigned leading_zeros = 0);

// Explicit instantiation declarations.
extern template struct EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT)
    MagicNumbersForDivision<uint32_t>;
extern template struct EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT)
    MagicNumbersForDivision<uint64_t>;

extern template EXPORT_TEMPLATE_DECLARE(…)
    MagicNumbersForDivision<uint32_t> SignedDivisionByConstant(uint32_t d);
extern template EXPORT_TEMPLATE_DECLARE(…)
    MagicNumbersForDivision<uint64_t> SignedDivisionByConstant(uint64_t d);

extern template EXPORT_TEMPLATE_DECLARE(…)
    MagicNumbersForDivision<uint32_t> UnsignedDivisionByConstant(
        uint32_t d, unsigned leading_zeros);
extern template EXPORT_TEMPLATE_DECLARE(…)
    MagicNumbersForDivision<uint64_t> UnsignedDivisionByConstant(
        uint64_t d, unsigned leading_zeros);

}  // namespace base
}  // namespace v8

#endif  // V8_BASE_DIVISION_BY_CONSTANT_H_