safe_op.hpp

// SPDX-License-Identifier: GPL-2.0-or-later
 
#ifndef SAFE_OP_HPP_
#define SAFE_OP_HPP_
 
#include <limits>
#include <stdexcept>
#include <type_traits>
 
#ifdef _MSC_VER
#include <Intsafe.h>
#endif

namespace Safe {
namespace Internal {
template <typename T>
bool fallback_add_overflow(T summand_1, T summand_2, T& result) {
  if constexpr (std::is_signed_v<T> && sizeof(T) >= sizeof(int)) {
    if (((summand_2 >= 0) && (summand_1 > std::numeric_limits<T>::max() - summand_2)) ||
        ((summand_2 < 0) && (summand_1 < std::numeric_limits<T>::min() - summand_2)))
      return true;
    result = summand_1 + summand_2;
    return false;
  } else if constexpr (std::is_signed_v<T> && sizeof(T) < sizeof(int)) {
    const int res = summand_1 + summand_2;
    if ((res > std::numeric_limits<T>::max()) || (res < std::numeric_limits<T>::min())) {
      return true;
    }
    result = static_cast<T>(res);
    return false;
  } else {
    result = summand_1 + summand_2;
    return result < summand_1;
  }
}

template <typename T>
bool builtin_add_overflow(T summand_1, T summand_2, T& result) {
  return fallback_add_overflow(summand_1, summand_2, result);
}
 
#if defined(__GNUC__) || defined(__clang__)
#if __GNUC__ >= 5 || __clang_major__ >= 3

#define SPECIALIZE_builtin_add_overflow(type, builtin_name)                                  \
  /* Full specialization of builtin_add_overflow for type using the */                       \
  /* builtin_name intrinsic */                                                               \
  template <>                                                                                \
  constexpr bool builtin_add_overflow<type>(type summand_1, type summand_2, type & result) { \
    return builtin_name(summand_1, summand_2, &result);                                      \
  }
 
SPECIALIZE_builtin_add_overflow(int, __builtin_sadd_overflow);
SPECIALIZE_builtin_add_overflow(long, __builtin_saddl_overflow);
SPECIALIZE_builtin_add_overflow(long long, __builtin_saddll_overflow);
 
SPECIALIZE_builtin_add_overflow(unsigned int, __builtin_uadd_overflow);
SPECIALIZE_builtin_add_overflow(unsigned long, __builtin_uaddl_overflow);
SPECIALIZE_builtin_add_overflow(unsigned long long, __builtin_uaddll_overflow);
 
#undef SPECIALIZE_builtin_add_overflow
#endif  // __GNUC__ >= 5 || __clang_major >= 3
 
#endif
 
}  // namespace Internal

template <typename T>
T add(T summand_1, T summand_2) {
  T res = 0;
  if (Internal::builtin_add_overflow(summand_1, summand_2, res)) {
    throw std::overflow_error("Overflow in addition");
  }
  return res;
}

template <typename T>
T abs(T num) noexcept {
  if constexpr (std::is_signed_v<T>) {
    if (num == std::numeric_limits<T>::min())
      return std::numeric_limits<T>::max();
    return num < 0 ? -num : num;
  }
  return num;
}
 
}  // namespace Safe
 
#endif  // SAFE_OP_HPP_