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// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_NUMERICS_WRAPPING_MATH_H_
#define BASE_NUMERICS_WRAPPING_MATH_H_
#include <type_traits>
namespace base {
// Returns `a + b` with overflow defined to wrap around, i.e. modulo 2^N where N
// is the bit width of `T`.
template <typename T>
inline constexpr T WrappingAdd(T a, T b) {
static_assert(std::is_integral_v<T>);
// Unsigned arithmetic wraps, so convert to the corresponding unsigned type.
// Note that, if `T` is smaller than `int`, e.g. `int16_t`, the values are
// promoted to `int`, which brings us back to undefined overflow. This is fine
// here because the sum of any two `int16_t`s fits in `int`, but `WrappingMul`
// will need a more complex implementation.
using Unsigned = std::make_unsigned_t<T>;
return static_cast<T>(static_cast<Unsigned>(a) + static_cast<Unsigned>(b));
}
// Returns `a - b` with overflow defined to wrap around, i.e. modulo 2^N where N
// is the bit width of `T`.
template <typename T>
inline constexpr T WrappingSub(T a, T b) {
static_assert(std::is_integral_v<T>);
// Unsigned arithmetic wraps, so convert to the corresponding unsigned type.
// Note that, if `T` is smaller than `int`, e.g. `int16_t`, the values are
// promoted to `int`, which brings us back to undefined overflow. This is fine
// here because the difference of any two `int16_t`s fits in `int`, but
// `WrappingMul` will need a more complex implementation.
using Unsigned = std::make_unsigned_t<T>;
return static_cast<T>(static_cast<Unsigned>(a) - static_cast<Unsigned>(b));
}
} // namespace base
#endif // BASE_NUMERICS_WRAPPING_MATH_H_
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