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// 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 {
static_assert(std::is_integral_v<T>);
MagicNumbersForDivision(T m, unsigned s, bool a)
: multiplier(m), shift(s), add(a) {}
bool operator==(const MagicNumbersForDivision& rhs) const {
return multiplier == rhs.multiplier && shift == rhs.shift && add == rhs.add;
}
T multiplier;
unsigned shift;
bool add;
};
// 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) {
using Unsigned = std::make_unsigned_t<T>;
MagicNumbersForDivision<Unsigned> magic =
SignedDivisionByConstant(static_cast<Unsigned>(d));
return {static_cast<T>(magic.multiplier), magic.shift, magic.add};
}
// 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(V8_BASE_EXPORT)
MagicNumbersForDivision<uint32_t> SignedDivisionByConstant(uint32_t d);
extern template EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT)
MagicNumbersForDivision<uint64_t> SignedDivisionByConstant(uint64_t d);
extern template EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT)
MagicNumbersForDivision<uint32_t> UnsignedDivisionByConstant(
uint32_t d, unsigned leading_zeros);
extern template EXPORT_TEMPLATE_DECLARE(V8_BASE_EXPORT)
MagicNumbersForDivision<uint64_t> UnsignedDivisionByConstant(
uint64_t d, unsigned leading_zeros);
} // namespace base
} // namespace v8
#endif // V8_BASE_DIVISION_BY_CONSTANT_H_
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