checked_arithmetic.h

// Copyright 2024 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once
 
#define PW_ADD_OVERFLOW(a, b, out) __builtin_add_overflow(a, b, out)
 
#define PW_SUB_OVERFLOW(a, b, out) __builtin_sub_overflow(a, b, out)
 
#define PW_MUL_OVERFLOW(a, b, out) __builtin_mul_overflow(a, b, out)
 
#ifdef __cplusplus
 
#include <cstdint>
#include <limits>
#include <optional>
#include <type_traits>
 
namespace pw {
 
 
template <typename A, typename B, typename T>
[[nodiscard]] constexpr bool CheckedAdd(A a, B b, T& result) {
  T temp = 0;
 
  if (PW_ADD_OVERFLOW(a, b, &temp)) {
    return false;
  }
  result = temp;
 
  return true;
}
 
template <typename T, typename A, typename B>
[[nodiscard]] constexpr std::optional<T> CheckedAdd(A a, B b) {
  T result{0};
 
  if (!CheckedAdd(a, b, result)) {
    return std::nullopt;
  }
 
  return result;
}
 
template <typename T, typename Inc>
[[nodiscard]] constexpr bool CheckedIncrement(T& base, Inc inc) {
  return CheckedAdd(base, inc, base);
}
 
template <typename A, typename B, typename T>
[[nodiscard]] constexpr bool CheckedSub(A a, B b, T& result) {
  T temp = 0;
 
  if (PW_SUB_OVERFLOW(a, b, &temp)) {
    return false;
  }
  result = temp;
 
  return true;
}
 
template <typename T, typename A, typename B>
[[nodiscard]] constexpr std::optional<T> CheckedSub(A a, B b) {
  T result{0};
 
  if (!CheckedSub(a, b, result)) {
    return std::nullopt;
  }
 
  return result;
}
 
template <typename T, typename Dec>
[[nodiscard]] constexpr bool CheckedDecrement(T& base, Dec dec) {
  return CheckedSub(base, dec, base);
}
 
template <typename A, typename B, typename T>
[[nodiscard]] constexpr bool CheckedMul(A a, B b, T& result) {
  T temp = 0;
 
  if (PW_MUL_OVERFLOW(a, b, &temp)) {
    return false;
  }
  result = temp;
 
  return true;
}
 
template <typename T, typename A, typename B>
[[nodiscard]] constexpr std::optional<T> CheckedMul(A a, B b) {
  T result{0};
 
  if (!CheckedMul(a, b, result)) {
    return std::nullopt;
  }
 
  return result;
}
 
}  // namespace pw
 
#endif  // __cplusplus