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xo-unit: + Quantity.subtract support

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This commit is contained in:
Roland Conybeare 2024-04-23 15:39:42 -04:00
commit dcf1439005
2 changed files with 74 additions and 0 deletions
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35
include/xo/unit/Quantity.hpp
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@ -110,6 +110,31 @@ namespace xo {
}
}
template <typename Quantity2>
static constexpr
auto subtract(const Quantity & x, const Quantity2 & y) {
using r_repr_type = std::common_type_t<typename Quantity::repr_type,
typename Quantity2::repr_type>;
using r_int_type = std::common_type_t<typename Quantity::ratio_int_type,
typename Quantity2::ratio_int_type>;
/* conversion to get y in same units as x: multiply by y/x */
auto rr = detail::nu_ratio(y.unit(), x.unit());
if (rr.natural_unit_.is_dimensionless()) {
r_repr_type r_scale = (static_cast<r_repr_type>(x.scale())
- (::sqrt(rr.outer_scale_sq_)
* rr.outer_scale_exact_.template to<r_repr_type>()
* static_cast<r_repr_type>(y.scale())));
return Quantity<r_repr_type, r_int_type>(r_scale, x.unit_.template to_repr<r_int_type>());
} else {
/* units don't match! */
return Quantity<r_repr_type, r_int_type>(std::numeric_limits<Repr>::quiet_NaN(),
x.unit_.template to_repr<r_int_type>());
}
}
private:
/** @brief quantity represents this multiple of a unit amount **/
Repr scale_ = Repr{};
@ -167,6 +192,16 @@ namespace xo {
return Quantity::add(x, y);
}
/** note: won't have constexpr result until c++26 (when ::sqrt(), ::pow() are constexpr)
**/
template <typename Quantity, typename Quantity2>
requires quantity2_concept<Quantity> && quantity2_concept<Quantity2>
constexpr auto
operator- (const Quantity & x, const Quantity2 & y)
{
return Quantity::subtract(x, y);
}
namespace unit {
constexpr auto nanogram = natural_unit_qty(nu2::nanogram);
}