Numeric.h

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/* Copyright (c) 2024 Skyward Experimental Rocketry
 * Authors: Niccolò Betto, Damiano Procaccia
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
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 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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 */
 
#pragma once
 
#include <cstring>
#include <limits>
#include <type_traits>
 
namespace detail
{
template <class T>
auto add_sat(T x, T y) noexcept ->
    typename std::enable_if_t<std::is_integral<T>::value, T>
{
    auto result = T{};
    // The built-in function returns true if the addition overflows
    bool overflow = __builtin_add_overflow(x, y, &result);
 
    if (!overflow)
        return result;
 
    if (x < 0)
        return std::numeric_limits<T>::min();
    else
        return std::numeric_limits<T>::max();
}
 
template <typename To, typename From>
auto bit_cast(const From& src) noexcept ->
    typename std::enable_if_t<sizeof(To) == sizeof(From) &&
                                  std::is_trivially_copyable<To>::value &&
                                  std::is_trivially_copyable<From>::value,
                              To>
{
    static_assert(std::is_trivially_constructible<To>::value,
                  "This implementation additionally requires "
                  "destination type to be trivially constructible");
 
    To dst;
    std::memcpy(&dst, &src, sizeof(To));
    return dst;
}
 
}  // namespace detail
 
namespace std
{
// C++20
#if __cplusplus < 202002L
 
using detail::bit_cast;
 
#endif
 
// C++26 (TODO: change to < 2026xxL when released)
#if __cplusplus <= 202302L
 
using detail::add_sat;
 
#endif
 
}  // namespace std