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xo-unit: quantity: + subtraction operator

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This commit is contained in:
Roland Conybeare 2024-05-04 15:11:16 -04:00
commit 8d5fcda096
1 changed files with 41 additions and 0 deletions
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41
include/xo/unit/quantity.hpp
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@ -266,6 +266,34 @@ namespace xo {
return quantity<x.s_unit, r_repr_type, r_int2x_type>(std::numeric_limits<r_repr_type>::quiet_NaN());
}
}
template <typename Q1, typename Q2>
requires(quantity_concept<Q1>
&& quantity_concept<Q2>
&& Q1::always_constexpr_unit
&& Q2::always_constexpr_unit)
static constexpr auto subtract(Q1 x, Q2 y) {
using r_repr_type = std::common_type_t<typename Q1::repr_type,
typename Q2::repr_type>;
using r_int_type = std::common_type_t<typename Q1::ratio_int_type,
typename Q2::ratio_int_type>;
using r_int2x_type = std::common_type_t<typename Q1::ratio_int2x_type,
typename Q2::ratio_int2x_type>;
/* conversion to get y in same units as x: multiply by y/x */
auto rr = detail::su_ratio<r_int_type, r_int2x_type>(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_factor_.template convert_to<r_repr_type>()
* static_cast<r_repr_type>(y.scale())));
return quantity<x.s_unit, r_repr_type, r_int2x_type>(r_scale);
} else {
/* units don't match! */
return quantity<x.s_unit, r_repr_type, r_int2x_type>(std::numeric_limits<r_repr_type>::quiet_NaN());
}
}
};
} /*namespace detail*/
@ -336,6 +364,19 @@ namespace xo {
return detail::quantity_util::add(x, y);
}
/** note: won't have constexpr result w/ fractional dimension until c++26 (when ::sqrt(), ::pow() are constexpr)
**/
template <typename Q1, typename Q2>
requires (quantity_concept<Q1>
&& quantity_concept<Q2>
&& Q1::always_constexpr_unit
&& Q2::always_constexpr_unit)
constexpr auto
operator- (const Q1 & x, const Q2 & y)
{
return detail::quantity_util::subtract(x, y);
}
namespace qty {
// ----- mass -----