convert_impl.hpp

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/* Copyright (C) 2022 Davide Faconti, Eurecat -  All Rights Reserved
*
*   Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"),
*   to deal in the Software without restriction, including without limitation the rights 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 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
*   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
*   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
 
#pragma once
 
#include <type_traits>
#include <cmath>
#include "simple_string.hpp"
 
#undef max
#undef min
 
namespace SafeAny
{
 
namespace details
{
 
template <typename BoolCondition>
using EnableIf = typename std::enable_if<BoolCondition::value, void>::type;
 
template <typename T>
constexpr bool is_integer()
{
  return std::is_same<T, bool>::value || std::is_same<T, char>::value ||
         std::is_integral<T>::value;
}
 
template <typename T>
constexpr bool is_convertible_type()
{
  return is_integer<T>() || std::is_floating_point<T>::value ||
         std::is_same<T, std::string>::value || std::is_same<T, SimpleString>::value ||
         std::is_enum<T>::value;
}
 
template <typename T>
constexpr bool is_convertible_to_bool()
{
  return is_integer<T>() || std::is_floating_point<T>::value || std::is_enum<T>::value;
}
 
template <typename T>
constexpr bool is_signed()
{
  return std::is_signed<T>::value;
}
 
template <typename T1, typename T2>
constexpr bool is_same()
{
  return std::is_same<T1, T2>::value;
}
 
template <typename From, typename To>
inline void checkUpperLimit(const From& from)
{
  if(from > static_cast<From>(std::numeric_limits<To>::max()))
  {
    throw std::runtime_error("Value outside the max numerical limit.");
  }
}
 
template <typename From, typename To>
inline void checkLowerLimit(const From& from)
{
  if constexpr(std::is_same<To, bool>::value)
  {
    if(from != 0 && from != 1)
    {
      throw std::runtime_error("Implicit casting to bool is not allowed");
    }
  }
  else if(from < std::numeric_limits<To>::min())
  {
    throw std::runtime_error("Value outside the lovest numerical limit.");
  }
}
 
template <typename From, typename To>
inline void checkTruncation(const From& from)
{
  // Handle integer to floating point
  if constexpr(std::is_integral_v<From> && std::is_floating_point_v<To>)
  {
    // Check if value can be represented exactly in the target type
    constexpr uint64_t max_exact = (1LL << std::numeric_limits<double>::digits) - 1;
    bool doesnt_fit = false;
    if constexpr(!std::is_signed_v<From>)
    {
      doesnt_fit = static_cast<uint64_t>(from) > max_exact;
    }
    else
    {
      doesnt_fit = std::abs(static_cast<int64_t>(from)) > static_cast<int64_t>(max_exact);
    }
    if(doesnt_fit)
    {
      throw std::runtime_error("Loss of precision when converting a large integer number "
                               "to floating point:" +
                               std::to_string(from));
    }
  }
  // Handle floating point to integer
  else if constexpr(std::is_floating_point_v<From> && std::is_integral_v<To>)
  {
    if(from > static_cast<From>(std::numeric_limits<To>::max()) ||
       from < static_cast<From>(std::numeric_limits<To>::lowest()) ||
       from != std::nearbyint(from))
    {
      throw std::runtime_error("Invalid floating point to integer conversion");
    }
  }
  // Handle other conversions
  else
  {
    if(from > static_cast<From>(std::numeric_limits<To>::max()) ||
       from < static_cast<From>(std::numeric_limits<To>::lowest()))
    {
      throw std::runtime_error("Value outside numeric limits");
    }
    To as_target = static_cast<To>(from);
    From back_to_source = static_cast<From>(as_target);
    if(from != back_to_source)
    {
      throw std::runtime_error("Value truncated in conversion");
    }
  }
}
 
//----------------------- Implementation ----------------------------------------------
 
template <typename SRC, typename DST>
void convertNumber(const SRC& source, DST& target)
{
  static_assert(is_convertible_type<SRC>() && is_convertible_type<DST>(), "Not "
                                                                          "convertible");
 
  constexpr bool both_integers = is_integer<SRC>() && is_integer<DST>();
 
  if constexpr(is_signed<SRC>() && !is_signed<DST>())
  {
    if(source < 0)
    {
      throw std::runtime_error("Value is negative and can't be converted to unsigned");
    }
  }
  // these conversions are always safe:
  // - same type
  // - float -> double
  if constexpr(is_same<SRC, DST>() || (is_same<SRC, float>() && is_same<DST, double>()))
  {
    // No check needed
    target = static_cast<DST>(source);
  }
  else if constexpr(both_integers)
  {
    if constexpr(sizeof(SRC) == sizeof(DST) && !is_signed<SRC>() && is_signed<DST>())
    {
      checkUpperLimit<SRC, DST>(source);
    }
    // casting to a smaller number need to be check
    else if constexpr(sizeof(SRC) > sizeof(DST))
    {
      if constexpr(is_signed<SRC>())
      {
        checkLowerLimit<SRC, DST>(source);
      }
      checkUpperLimit<SRC, DST>(source);
    }
    target = static_cast<DST>(source);
  }
  // special case: bool accept truncation
  else if constexpr(is_convertible_to_bool<SRC>() && is_same<DST, bool>())
  {
    target = static_cast<DST>(source);
  }
  // casting to/from floating points might cause truncation.
  else if constexpr(std::is_floating_point<SRC>::value ||
                    std::is_floating_point<DST>::value)
  {
    bool both_float =
        std::is_floating_point<SRC>::value && std::is_floating_point<DST>::value;
    // to avoid being too pedantic, let's accept casting between double and float
    if(!both_float)
    {
      checkTruncation<SRC, DST>(source);
    }
    target = static_cast<DST>(source);
  }
}
 
}  //end namespace details
}  //end namespace SafeAny