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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);
}

39
utest/unit.test.cpp
View file

@ -1158,6 +1158,45 @@ namespace xo {
//REQUIRE(ng2.scale() == 1);
} /*TEST_CASE(Quantity6)*/
TEST_CASE("Quantity7", "[Quantity]") {
constexpr bool c_debug_flag = true;
// can get bits from /dev/random by uncommenting the 2nd line below
//uint64_t seed = xxx;
//rng::Seed<xoshio256ss> seed;
//auto rng = xo::rng::xoshiro256ss(seed);
scope log(XO_DEBUG2(c_debug_flag, "TEST_CASE.Quantity7"));
//log && log("(A)", xtag("foo", foo));
/* not constexpr until c++26 */
Quantity ng = unit_qty(su2::nanogram);
Quantity ug = unit_qty(su2::microgram);
{
auto sum1 = ng - ug;
log && log(xtag("ng-ug", sum1));
/* units will be nanograms, since that's on lhs */
REQUIRE(sum1.unit().n_bpu() == 1);
REQUIRE(sum1.unit()[0].scalefactor() == scalefactor_ratio_type(1, 1000000000));
REQUIRE(sum1.scale() == -999.0);
}
{
auto sum2 = ug - ng;
log && log(xtag("ug-ng", sum2));
/* units will be micrograms, since that's on rhs */
REQUIRE(sum2.unit().n_bpu() == 1);
REQUIRE(sum2.unit()[0].scalefactor() == scalefactor_ratio_type(1, 1000000));
REQUIRE(sum2.scale() == 0.999);
}
//REQUIRE(ng2.scale() == 1);
} /*TEST_CASE(Quantity7)*/
} /*namespace ut*/
} /*namespace xo*/