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Use Magnitude implementation for base_units_ratio

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This resolves a TODO and lets us use arbitrary exponent denominators.

I also attempt to clarify the semantics.  This is based on my best
effort of understanding pre-existing concepts in the library, so I hope
I got it right!
This commit is contained in:
Chip Hogg
2022-04-09 17:49:39 +00:00
parent 5c0eb0667c
commit 5afe7766e9
1 changed files with 17 additions and 11 deletions
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28
src/core/include/units/bits/base_units_ratio.h
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@@ -24,29 +24,35 @@
#include <units/base_dimension.h>
#include <units/exponent.h>
#include <units/magnitude.h>
#include <units/ratio.h>
namespace units::detail {
template<Exponent E>
requires(E::den == 1 || E::den == 2) // TODO provide support for any den
constexpr ratio exp_ratio()
/**
* @brief Calculates the "absolute" magnitude of the derived dimension defined by this list.
*
* "Absolute" magnitudes are not physically observable: only ratios of magnitudes are. For example: if we multiplied
* all magnitudes in the system by the same constant, no meaningful results would change. However, in practice, we need
* to make some global choice for the "absolute" values of magnitudes, so that we can compute their ratios.
*
* The point of this function is to compute the absolute magnitude of a derived dimension, in terms of the absolute
* magnitudes of its constituent dimensions.
*/
template<typename... Es>
constexpr Magnitude auto absolute_magnitude(exponent_list<Es...>)
{
const ratio base_ratio = E::dimension::base_unit::ratio;
const ratio positive_ratio =
E::num * E::den < 0 ? ratio(base_ratio.den, base_ratio.num, -base_ratio.exp) : base_ratio;
const std::intmax_t N = E::num * E::den < 0 ? -E::num : E::num;
const ratio ratio_pow = pow<N>(positive_ratio);
return E::den == 2 ? sqrt(ratio_pow) : ratio_pow;
return (pow<ratio{Es::num, Es::den}>(Es::dimension::base_unit::mag) * ... * magnitude<>{});
}
/**
* @brief Calculates the common ratio of all the references of base units in the derived dimension
*/
template<typename... Es>
constexpr ratio base_units_ratio(exponent_list<Es...>)
constexpr ratio base_units_ratio(exponent_list<Es...> es)
{
return (exp_ratio<Es>() * ... * ratio(1));
return as_ratio(absolute_magnitude(es));
}
} // namespace units::detail