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fix: performace regression in sudo_cast fixed

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Mateusz Pusz
2024-01-19 16:04:55 +01:00
parent fc7e1358cb
commit 840b0bd54e
1 changed files with 27 additions and 18 deletions
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45
src/core/include/mp-units/bits/sudo_cast.h
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@@ -30,17 +30,12 @@
namespace mp_units::detail {
// determines the best available representation type
template<Quantity From, Quantity To>
[[nodiscard]] consteval auto common_rep_type(From, To)
{
if constexpr (requires { typename std::common_type_t<typename From::rep, typename To::rep>; })
// returns a common type of two representation types if available
// e.g. `double` and `int` will end up with `double` precision
return std::common_type_t<typename From::rep, typename To::rep>{};
else
return typename From::rep{};
}
template<typename T, typename Other>
struct get_common_type : std::common_type<T, Other> {};
template<typename T, typename Other>
using maybe_common_type = MP_UNITS_TYPENAME std::conditional_t<requires { typename std::common_type_t<T, Other>; },
get_common_type<T, Other>, std::type_identity<T>>::type;
/**
* @brief Explicit cast between different quantity types
@@ -73,15 +68,29 @@ template<Quantity To, typename From>
constexpr Magnitude auto num = numerator(c_mag);
constexpr Magnitude auto den = denominator(c_mag);
constexpr Magnitude auto irr = c_mag * (den / num);
using c_rep_type = decltype(common_rep_type(q, To{}));
using c_rep_type = maybe_common_type<typename std::remove_reference_t<From>::rep, typename To::rep>;
using c_mag_type = common_magnitude_type<c_mag>;
using multiplier_type =
conditional<treat_as_floating_point<c_rep_type>, std::common_type_t<c_mag_type, long double>, c_mag_type>;
using multiplier_type = conditional<treat_as_floating_point<c_rep_type>,
// ensure that the multiplier is also floating-point
conditional<std::is_arithmetic_v<underlying_type_t<c_rep_type>>,
// reuse user's type if possible
std::common_type_t<c_mag_type, underlying_type_t<c_rep_type>>,
std::common_type_t<c_mag_type, double>>,
c_mag_type>;
using c_type = maybe_common_type<c_rep_type, multiplier_type>;
constexpr auto val = [](Magnitude auto m) { return get_value<multiplier_type>(m); };
return {static_cast<MP_UNITS_TYPENAME To::rep>(
static_cast<c_rep_type>(std::forward<From>(q).numerical_value_is_an_implementation_detail_) * val(num) /
val(den) * val(irr)),
To::reference};
if constexpr (std::is_floating_point_v<multiplier_type>) {
// this results in great assembly
constexpr auto ratio = val(num) / val(den) * val(irr);
auto res = static_cast<MP_UNITS_TYPENAME To::rep>(
static_cast<c_type>(q.numerical_value_is_an_implementation_detail_) * ratio);
return {res, To::reference};
} else {
// this is slower but allows conversions like 2000 m -> 2 km without loosing data
auto res = static_cast<MP_UNITS_TYPENAME To::rep>(
static_cast<c_type>(q.numerical_value_is_an_implementation_detail_) * val(num) / val(den) * val(irr));
return {res, To::reference};
}
}
}