/* See LICENSE file for copyright and license details. */
#include "libred.h"
#include <math.h>
#include <time.h>
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#if __GNUC__
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wunsuffixed-float-constants"
#endif
/* Select clock. */
#if defined(DO_NOT_USE_COARSEC_CLOCK) || !defined(CLOCK_REALTIME_COARSE)
# ifdef CLOCK_REALTIME_COARSE
# undef CLOCK_REALTIME_COARSE
# endif
# define CLOCK_REALTIME_COARSE CLOCK_REALTIME
#endif
/**
* Get current Julian Centuries time (100 Julian Days since J2000)
* and Julian Day time
*
* @param tc_out Output parameter for the current Julian Centuries time
* @param td_out Output parameter for the current Julian Day time
* @return 0 on success, -1 on failure
* @throws Any error specified for clock_gettime(3) on error
*/
static int
julian_time(double *tc_out, double *td_out)
{
struct timespec now;
double tu;
if (clock_gettime(CLOCK_REALTIME_COARSE, &now))
return -1;
tu = fma((double)now.tv_nsec, 0.000000001, (double)now.tv_sec);
*td_out = tu / 86400.0 + 2440587.5;
*tc_out = (*td_out - 2451545.0) / 36525.0;
return 0;
}
/**
* Convert an angle (or otherwise) from degrees to radians
*
* @param deg The angle in degrees
* @param The angle in radians
*/
static double
radians(double deg)
{
return (double)M_PI / 180.0 * deg;
}
/**
* Convert an angle (or otherwise) from radians to degrees
*
* @param rad The angle in radians
* @param The angle in degrees
*/
static double
degrees(double rad)
{
return 180.0 / (double)M_PI * rad;
}
/**
* Convert an angle (or otherwise) from degrees to radians
* and, using fused multply–add, add some number of degrees
*
* @param deg The angle in degrees
* @param aug The number of radians to add
* @param The angle in radians, plus `aug`
*/
static double
radians_plus(double deg, double aug)
{
return fma((double)M_PI / 180.0, deg, aug);
}
/**
* Convert an angle (or otherwise) from radians to degrees
* and, using fused multply–add, add some number of degrees
*
* @param rad The angle in radians
* @param aug The number of degrees to add
* @param The angle in degrees, plus `aug`
*/
static double
degrees_plus(double rad, double aug)
{
return fma(180.0 / (double)M_PI, rad, aug);
}
/**
* Calculates the Sun's elevation from the solar hour angle
*
* @param latitude The latitude in degrees northwards from
* the equator, negative for southwards
* @param declination The declination, in radians
* @param hour_angle The solar hour angle, in radians
* @return The Sun's elevation, in radians
*/
static double
elevation_from_hour_angle(double latitude, double declination, double hour_angle)
{
double c, s;
latitude = radians(latitude);
c = cos(latitude) * cos(declination);
s = sin(latitude) * sin(declination);
return asin(fma(c, cos(hour_angle), s));
}
/**
* Calculates the Sun's geometric mean longitude
*
* @param t The time in Julian Centuries
* @return The Sun's geometric mean longitude in radians
*/
static double
sun_geometric_mean_longitude(double t)
{
return radians(fmod(fma(fma(0.0003032, t, 36000.76983), t, 280.46646), 360.0));
}
/**
* Calculates the Sun's geometric mean anomaly
*
* @param t The time in Julian Centuries
* @return The Sun's geometric mean anomaly in radians
*/
static double
sun_geometric_mean_anomaly(double t)
{
return radians(fmod(fma(fma(-0.0001537, t, 35999.05029), t, 357.52911), 360.0));
}
/**
* Calculates the Earth's orbit eccentricity
*
* @param t The time in Julian Centuries
* @return The Earth's orbit eccentricity
*/
static double
earth_orbit_eccentricity(double t)
{
return fma(fma(-0.0000001267, t, -0.000042037), t, 0.016708634);
}
/**
* Calculates the Sun's equation of the centre, the difference
* between the true anomaly and the mean anomaly
*
* @param t The time in Julian Centuries
* @return The Sun's equation of the centre, in radians
*/
static double
sun_equation_of_centre(double t)
{
double a = sun_geometric_mean_anomaly(t), r;
r = sin(1.0 * a) * fma(fma(-0.000014, t, 0.004817), t, 1.914602);
r = fma(sin(2.0 * a), fma(-0.000101, t, 0.019993), r);
r = fma(sin(3.0 * a), 0.000289, r);
return radians(r);
}
/**
* Calculates the Sun's real longitudinal position
*
* @param t The time in Julian Centuries
* @return The longitude, in radians
*/
static double
sun_real_longitude(double t)
{
return sun_geometric_mean_longitude(t) + sun_equation_of_centre(t);
}
/**
* Calculates the Sun's apparent longitudinal position
*
* @param t The time in Julian Centuries
* @return The longitude, in radians
*/
static double
sun_apparent_longitude(double t)
{
double r = degrees_plus(sun_real_longitude(t), -0.00569);
double a = radians(fma(-1934.136, t, 125.04));
return radians(fma(-0.00478, sin(a), r));
}
/**
* Calculates the mean ecliptic obliquity of the Sun's
* apparent motion without variation correction
*
* @param t The time in Julian Centuries
* @return The uncorrected mean obliquity, in radians
*/
static double
mean_ecliptic_obliquity(double t)
{
double r = fma(fma(fma(0.001813, t, -0.00059), t, -46.815), t, 21.448);
return radians(23.0 + (26.0 + r / 60.0) / 60.0);
}
/**
* Calculates the mean ecliptic obliquity of the Sun's
* parent motion with variation correction
*
* @param t The time in Julian Centuries
* @return The mean obliquity, in radians
*/
static double
corrected_mean_ecliptic_obliquity(double t)
{
double r = cos(radians(fma(-1934.136, t, 125.04)));
return radians_plus(0.00256 * r, mean_ecliptic_obliquity(t));
}
/**
* Calculates the Sun's declination
*
* @param t The time in Julian Centuries
* @return The Sun's declination, in radian
*/
static double
solar_declination(double t)
{
double r = sin(corrected_mean_ecliptic_obliquity(t));
return asin(r * sin(sun_apparent_longitude(t)));
}
/**
* Calculates the equation of time, the discrepancy
* between apparent and mean solar time
*
* @param t The time in Julian Centuries
* @return The equation of time, in degrees
*/
static double
equation_of_time(double t)
{
double l = sun_geometric_mean_longitude(t);
double e = earth_orbit_eccentricity(t);
double m = sun_geometric_mean_anomaly(t);
double y = pow(tan(corrected_mean_ecliptic_obliquity(t) / 2.0), 2.0);
double r, c, s;
s = y * sin(2.0 * l);
c = y * cos(2.0 * l);
r = fma(fma(4.0, c, -2.0), e * sin(m), s);
r = fma(pow(0.50 * y, 2.0), sin(-4.0 * l), r);
r = fma(pow(1.25 * e, 2.0), sin(-2.0 * m), r);
return 4.0 * degrees(r);
}
/**
* Calculates the Sun's elevation as apparent
* from a geographical position
*
* @param tc The time in Julian Centuries
* @param td The time in Julian Days
* @param latitude The latitude in degrees northwards from
* the equator, negative for southwards
* @param longitude The longitude in degrees eastwards from
* Greenwich, negative for westwards
* @return The Sun's apparent elevation at the specified time as seen
* from the specified position, measured in radians
*/
static double
solar_elevation_from_time(double tc, double td, double latitude, double longitude)
{
double r;
td = td - round(td);
r = fma(1440, td - 1, -equation_of_time(tc));
r = radians(fma(0.25, r, -longitude));
return elevation_from_hour_angle(latitude, solar_declination(tc), r);
}
/**
* Calculates the Sun's elevation as apparent
* from a geographical position
*
* @param latitude The latitude in degrees northwards from
* the equator, negative for southwards
* @param longitude The longitude in degrees eastwards from
* Greenwich, negative for westwards
* @param elevation Output parameter for the Sun's apparent elevation
* as seen, right now, from the specified position,
* measured in degrees
* @return 0 on success, -1 on failure
* @throws Any error specified for clock_gettime(3) on error
*/
double
libred_solar_elevation(double latitude, double longitude, double *elevation)
{
double tc, td;
if (julian_time(&tc, &td))
return -1;
*elevation = degrees(solar_elevation_from_time(tc, td, latitude, longitude));
return 0;
}
/**
* This function is obsolete
*/
int
libred_check_timetravel(void)
{
return 0;
}
