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Introduce mixed_sign_less()/min()/max() (#18)

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Previously, there was mixed sign comparison:
```
reflected_min_v = -120 > 0U ? -120 : 0
```
which returns -120 because the condition is true, since the
compiler casts the signed value to unsigned, leading to a huge value.
This caused the following values as result:

```
reflected_min_v == -120
min_v = -1
static_cast<U>(min_v) = 18446744073709551615
```

The last one is used in magic_enum::enum_index().
This commit is contained in:
Alexander Karatarakis 2019-10-14 00:44:09 -07:00 • committed by Daniil Goncharov
parent 1f3ea64407
commit 0f36cd5b0f
2 changed files with 114 additions and 6 deletions
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36
include/magic_enum.hpp
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@ -141,6 +141,34 @@ constexpr std::string_view pretty_name(std::string_view name) noexcept {
return {}; // Invalid name.
}
template<typename L, typename R>
constexpr bool mixed_sign_less(L left, R right) noexcept {
static_assert(std::is_integral_v<L>, "L must be an integral value");
static_assert(std::is_integral_v<R>, "R must be an integral value");
if constexpr(std::is_signed_v<L> == std::is_signed_v<R>) {
// If same signedness (both signed or both unsigned)
return left < right;
}
else if constexpr(std::is_signed_v<L>) {
// if 'left' is negative, then result is 'true', otherwise cast & compare
return left < 0 || static_cast<std::make_unsigned_t<L>>(left) < right;
}
else { // std::is_signed_v<R>
// if 'right' is negative, then result is 'false', otherwise cast & compare
return right >= 0 && left < static_cast<std::make_unsigned_t<R>>(right);
}
}
template<typename L, typename R>
constexpr int mixed_sign_min_as_int(L left, R right) noexcept {
return mixed_sign_less(left, right) ? static_cast<int>(left) : static_cast<int>(right);
}
template<typename L, typename R>
constexpr int mixed_sign_max_as_int(L left, R right) noexcept {
return mixed_sign_less(left, right) ? static_cast<int>(right) : static_cast<int>(left);
}
template <typename E>
constexpr auto n() noexcept {
static_assert(is_enum_v<E>, "magic_enum::detail::n requires enum type.");
@ -182,14 +210,10 @@ template <typename E, E V>
inline constexpr auto name_v = n<E, V>();
template <typename E>
inline constexpr int reflected_min_v = static_cast<int>(enum_range<E>::min > (std::numeric_limits<std::underlying_type_t<E>>::min)()
? enum_range<E>::min
: (std::numeric_limits<std::underlying_type_t<E>>::min)());
inline constexpr int reflected_min_v = mixed_sign_max_as_int(enum_range<E>::min, std::numeric_limits<std::underlying_type_t<E>>::min());
template <typename E>
inline constexpr int reflected_max_v = static_cast<int>(enum_range<E>::max < (std::numeric_limits<std::underlying_type_t<E>>::max)()
? enum_range<E>::max
: (std::numeric_limits<std::underlying_type_t<E>>::max)());
inline constexpr int reflected_max_v = mixed_sign_min_as_int(enum_range<E>::max, std::numeric_limits<std::underlying_type_t<E>>::max());
template <typename E>
constexpr std::size_t reflected_size() {