angles.hpp

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// SPDX-License-Identifier: BSD-3-Clause
// Copyright (C) 2026 Vallés Puig, Ramon
 
#pragma once
 
#include <cmath>
#include <type_traits>
 
#include "ffi_core.hpp"
#include "units/angular.hpp"
 
namespace qtty {
 
template <class Tag> struct AngularTraits {
  static constexpr bool is_angular = false;
};
 
#define QTTY_MARK_ANGULAR(Tag)                                                                     \
  template <> struct AngularTraits<Tag> {                                                          \
    static constexpr bool is_angular = true;                                                       \
  }
 
QTTY_MARK_ANGULAR(MilliradianTag);
QTTY_MARK_ANGULAR(RadianTag);
QTTY_MARK_ANGULAR(MicroArcsecondTag);
QTTY_MARK_ANGULAR(MilliArcsecondTag);
QTTY_MARK_ANGULAR(ArcsecondTag);
QTTY_MARK_ANGULAR(ArcminuteTag);
QTTY_MARK_ANGULAR(DegreeTag);
QTTY_MARK_ANGULAR(GradianTag);
QTTY_MARK_ANGULAR(TurnTag);
QTTY_MARK_ANGULAR(HourAngleTag);
 
#undef QTTY_MARK_ANGULAR
 
template <class Tag> inline constexpr bool is_angular_v = AngularTraits<Tag>::is_angular;
 
template <class Tag> inline auto sin(Quantity<Tag> a) {
  static_assert(is_angular_v<Tag>, "sin requires an angular quantity");
  return std::sin(a.template to<RadianTag>().value());
}
 
template <class Tag> inline auto cos(Quantity<Tag> a) {
  static_assert(is_angular_v<Tag>, "cos requires an angular quantity");
  return std::cos(a.template to<RadianTag>().value());
}
 
template <class Tag> inline auto tan(Quantity<Tag> a) {
  static_assert(is_angular_v<Tag>, "tan requires an angular quantity");
  return std::tan(a.template to<RadianTag>().value());
}
 
namespace detail {
 
inline double rem_euclid(double a, double b) {
  double r = std::fmod(a, b);
  return (r < 0.0) ? r + std::abs(b) : r;
}
 
} // namespace detail
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline double angular_full_turn() {
  constexpr double tau = 6.283185307179586476925286766559;
  return Quantity<RadianTag>(tau).template to<Tag>().value();
}
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline Quantity<Tag> wrap_pos(Quantity<Tag> a) {
  return Quantity<Tag>(detail::rem_euclid(a.value(), angular_full_turn<Tag>()));
}
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline Quantity<Tag> normalize(Quantity<Tag> a) {
  return wrap_pos(a);
}
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline Quantity<Tag> wrap_signed(Quantity<Tag> a) {
  double full = angular_full_turn<Tag>();
  double half = 0.5 * full;
  double y = detail::rem_euclid(a.value() + half, full) - half;
  double norm = (y <= -half) ? y + full : y;
  return Quantity<Tag>(norm);
}
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline Quantity<Tag> wrap_signed_lo(Quantity<Tag> a) {
  double full = angular_full_turn<Tag>();
  double half = 0.5 * full;
  double y = wrap_signed(a).value();
  if (y >= half) {
    y -= full;
  }
  return Quantity<Tag>(y);
}
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline Quantity<Tag> wrap_quarter_fold(Quantity<Tag> a) {
  double full = angular_full_turn<Tag>();
  double half = 0.5 * full;
  double quarter = 0.25 * full;
  double y = detail::rem_euclid(a.value() + quarter, full);
  return Quantity<Tag>(quarter - std::abs(y - half));
}
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline Quantity<Tag> signed_separation(Quantity<Tag> a, Quantity<Tag> b) {
  return wrap_signed(a - b);
}
 
template <class Tag, class = std::enable_if_t<is_angular_v<Tag>>>
inline Quantity<Tag> abs_separation(Quantity<Tag> a, Quantity<Tag> b) {
  return Quantity<Tag>(std::abs(signed_separation(a, b).value()));
}
 
} // namespace qtty