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Refactor BasePower struct and concept

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Instead of templating on `long double`, we template on "anything whose
value member is `long double`".  This is how we work around gcc-10's
lack of support for floating point NTTPs.

To access the base value, we provide `.get_base()` member functions.

The clearest and most direct way I know to express "is this a base
power" is via a type trait, which is true only for `base_power<T>`.
This commit is contained in:
Chip Hogg
2022-01-08 14:40:28 -05:00
parent 3063aebe5a
commit 9d48e6983a
1 changed files with 20 additions and 5 deletions
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25
src/core/include/units/magnitude.h
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@@ -44,7 +44,7 @@ constexpr bool is_prime(std::intmax_t n);
// Integer rep is for prime numbers; long double is for any irrational base we permit.
template<typename T>
concept BaseRep = std::is_same_v<T, int> || std::is_same_v<T, long double>;
concept BaseRep = std::is_same_v<T, int> || std::is_same_v<T::value, long double>;
/**
* @brief A basis vector in our magnitude representation, raised to some rational power.
@@ -60,11 +60,21 @@ concept BaseRep = std::is_same_v<T, int> || std::is_same_v<T, long double>;
*/
template<BaseRep T>
struct base_power {
// The value of the basis vector.
T base;
// The rational power to which the base is raised.
ratio power{1};
constexpr long double get_base() const { return T::value; }
};
template<>
struct base_power<int> {
// The value of the basis "vector".
int base;
// The rational power to which the base is raised.
ratio power{1};
constexpr int get_base() const { return base; }
};
template<BaseRep T, std::convertible_to<ratio> U>
@@ -94,10 +104,15 @@ constexpr bool is_valid_base_power(const base_power<T> &bp) {
else if constexpr (std::is_same_v<T, long double>) { return bp.base > 0; }
else { return false; } // Unreachable.
}
template<typename T>
struct is_base_power : std::false_type {};
template<BaseRep T>
struct is_base_power<base_power<T>> : std::true_type {};
} // namespace detail
template<typename T>
concept BasePower = std::is_same_v<T, base_power<int>> || std::is_same_v<T, base_power<long double>>;
concept BasePower = detail::is_base_power<T>::value;
/**
* @brief A representation for positive real numbers which optimizes taking products and rational powers.
@@ -107,7 +122,7 @@ concept BasePower = std::is_same_v<T, base_power<int>> || std::is_same_v<T, base
*/
template<BasePower auto... BasePowers>
requires requires {
// (is_valid_base_power(BasePowers) && ... && strictly_increasing(std::make_tuple(BasePowers.base...)));
// (is_valid_base_power(BasePowers) && ... && strictly_increasing(BasePowers.base...));
(detail::is_valid_base_power(BasePowers) && ...);
}
struct magnitude {};