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