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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 namespace gurl_base { // Returns `a + b` with overflow defined to wrap around, i.e. modulo 2^N where N // is the bit width of `T`. template inline constexpr T WrappingAdd(T a, T b) { static_assert(std::is_integral_v); // 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; return static_cast(static_cast(a) + static_cast(b)); } // Returns `a - b` with overflow defined to wrap around, i.e. modulo 2^N where N // is the bit width of `T`. template inline constexpr T WrappingSub(T a, T b) { static_assert(std::is_integral_v); // 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; return static_cast(static_cast(a) - static_cast(b)); } } // namespace base #endif // BASE_NUMERICS_WRAPPING_MATH_H_