diff options
Diffstat (limited to 'solar.c')
| -rw-r--r-- | solar.c | 258 |
1 files changed, 133 insertions, 125 deletions
@@ -3,6 +3,7 @@ #include <math.h> #include <time.h> #include <errno.h> +#include <stdint.h> #include <stdio.h> #include <stdlib.h> @@ -21,228 +22,250 @@ /** - * Get current Julian Centuries time (100 Julian days since J2000) + * Get current Julian Centuries time (100 Julian Days since J2000) + * and Julian Day time * - * @param nowp Output parameter for the current Julian Centuries time - * @return 0 on success, -1 on failure - * @throws Any error specified for clock_gettime(3) on error + * @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_centuries(double *nowp) +julian_time(double *tc_out, double *td_out) { struct timespec now; + double tu; if (clock_gettime(CLOCK_REALTIME_COARSE, &now)) return -1; - *nowp = (double)(now.tv_nsec) / 1000000000.0 + (double)(now.tv_sec); - *nowp = (*nowp / 86400.0 + 2440587.5 - 2451545.0) / 36525.0; + 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 a Julian Centuries timestamp to a Julian Day timestamp + * Convert an angle (or otherwise) from degrees to radians * - * @param tm The time in Julian Centuries - * @return The time in Julian Days + * @param deg The angle in degrees + * @param The angle in radians */ -static inline double -julian_centuries_to_julian_day(double tm) +static double +radians(double deg) { - return tm * 36525.0 + 2451545.0; + 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 The angle in radians. + * @param deg The angle in degrees + * @param aug The number of radians to add + * @param The angle in radians, plus `aug` */ -static inline double -radians(double deg) +static double +radians_plus(double deg, double aug) { - return deg * (double)M_PI / 180.0; + 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 The angle in degrees. + * @param rad The angle in radians + * @param aug The number of degrees to add + * @param The angle in degrees, plus `aug` */ -static inline double -degrees(double rad) +static double +degrees_plus(double rad, double aug) { - return rad * 180.0 / (double)M_PI; + return fma(180.0 / (double)M_PI, rad, aug); } /** * Calculates the Sun's elevation from the solar hour angle * - * @param longitude The longitude in degrees eastwards - * from Greenwich, negative for westwards + * @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 inline double +static double elevation_from_hour_angle(double latitude, double declination, double hour_angle) { - double rc = cos(radians(latitude)); - rc *= cos(hour_angle) * cos(declination); - rc += sin(radians(latitude)) * sin(declination); - return asin(rc); + 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 tm The time in Julian Centuries - * @return The Sun's geometric mean longitude in radians + * @param t The time in Julian Centuries + * @return The Sun's geometric mean longitude in radians */ -static inline double -sun_geometric_mean_longitude(double tm) +static double +sun_geometric_mean_longitude(double t) { - double rc = fmod(pow(0.0003032 * tm, 2.0) + 36000.76983 * tm + 280.46646, 360.0); -#if defined(TIMETRAVELLER) - rc = rc < 0.0 ? (rc + 360.0) : rc; -#endif - return radians(rc); + return radians(fmod(fma(fma(0.0003032, t, 36000.76983), t, 280.46646), 360.0)); } /** * Calculates the Sun's geometric mean anomaly * - * @param tm The time in Julian Centuries - * @return The Sun's geometric mean anomaly in radians + * @param t The time in Julian Centuries + * @return The Sun's geometric mean anomaly in radians */ -static inline double -sun_geometric_mean_anomaly(double tm) +static double +sun_geometric_mean_anomaly(double t) { - return radians(pow(-0.0001537 * tm, 2.0) + 35999.05029 * tm + 357.52911); + return radians(fmod(fma(fma(-0.0001537, t, 35999.05029), t, 357.52911), 360.0)); } /** * Calculates the Earth's orbit eccentricity * - * @param tm The time in Julian Centuries - * @return The Earth's orbit eccentricity + * @param t The time in Julian Centuries + * @return The Earth's orbit eccentricity */ -static inline double -earth_orbit_eccentricity(double tm) +static double +earth_orbit_eccentricity(double t) { - return pow(-0.0000001267 * tm, 2.0) - 0.000042037 * tm + 0.016708634; + 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 tm The time in Julian Centuries - * @return The Sun's equation of the centre, in radians + * @param t The time in Julian Centuries + * @return The Sun's equation of the centre, in radians */ -static inline double -sun_equation_of_centre(double tm) +static double +sun_equation_of_centre(double t) { - double a = sun_geometric_mean_anomaly(tm), rc; - rc = sin(1.0 * a) * (pow(-0.000014 * tm, 2.0) - 0.004817 * tm + 1.914602); - rc += sin(2.0 * a) * (-0.000101 * tm + 0.019993); - rc += sin(3.0 * a) * 0.000289; - return radians(rc); + 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 tm The time in Julian Centuries - * @return The longitude, in radians + * @param t The time in Julian Centuries + * @return The longitude, in radians */ -static inline double -sun_real_longitude(double tm) +static double +sun_real_longitude(double t) { - return sun_geometric_mean_longitude(tm) + sun_equation_of_centre(tm); + return sun_geometric_mean_longitude(t) + sun_equation_of_centre(t); } /** * Calculates the Sun's apparent longitudinal position * - * @param tm The time in Julian Centuries - * @return The longitude, in radians + * @param t The time in Julian Centuries + * @return The longitude, in radians */ -static inline double -sun_apparent_longitude(double tm) +static double +sun_apparent_longitude(double t) { - double rc = degrees(sun_real_longitude(tm)) - 0.00569; - return radians(rc - 0.00478 * sin(radians(-1934.136 * tm + 125.04))); + 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 tm The time in Julian Centuries - * @return The uncorrected mean obliquity, in radians + * @param t The time in Julian Centuries + * @return The uncorrected mean obliquity, in radians */ static double -mean_ecliptic_obliquity(double tm) +mean_ecliptic_obliquity(double t) { - double rc = pow(0.001813 * tm, 3.0) - pow(0.00059 * tm, 2.0) - 46.815 * tm + 21.448; - return radians(23.0 + (26.0 + rc / 60.0) / 60.0); + 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 tm The time in Julian Centuries - * @return The mean obliquity, in radians + * @param t The time in Julian Centuries + * @return The mean obliquity, in radians */ static double -corrected_mean_ecliptic_obliquity(double tm) +corrected_mean_ecliptic_obliquity(double t) { - double rc = 0.00256 * cos(radians(-1934.136 * tm + 125.04)); - return radians(rc + degrees(mean_ecliptic_obliquity(tm))); + 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 tm The time in Julian Centuries - * @return The Sun's declination, in radian + * @param t The time in Julian Centuries + * @return The Sun's declination, in radian */ -static inline double -solar_declination(double tm) +static double +solar_declination(double t) { - double rc = sin(corrected_mean_ecliptic_obliquity(tm)); - return asin(rc * sin(sun_apparent_longitude(tm))); + 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 tm The time in Julian Centuries - * @return The equation of time, in degrees + * @param t The time in Julian Centuries + * @return The equation of time, in minutes of time */ -static inline double -equation_of_time(double tm) +static double +equation_of_time(double t) { - double l = sun_geometric_mean_longitude(tm); - double e = earth_orbit_eccentricity(tm); - double m = sun_geometric_mean_anomaly(tm); - double y = pow(tan(corrected_mean_ecliptic_obliquity(tm) / 2.0), 2.0); - double rc = y * sin(2.0 * l); - rc += (4.0 * y * cos(2.0 * l) - 2.0) * e * sin(m); - rc -= pow(0.5 * y, 2.0) * sin(4.0 * l); - rc -= pow(1.25 * e, 2.0) * sin(2.0 * m); - return 4.0 * degrees(rc); + double l = sun_geometric_mean_longitude(t); + double e = earth_orbit_eccentricity(t); + double m = sun_geometric_mean_anomaly(t); + double y = tan(corrected_mean_ecliptic_obliquity(t) / 2.0; + double r, c, s; + y *= y; + 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(-0.5 * y*y, sin(4.0 * l), r); + r = fma(-1.25 * e*e, sin(2.0 * m), r); + return 4.0 * degrees(r); } /** * Calculates the Sun's elevation as apparent * from a geographical position * - * @param tm The time in Julian Centuries + * @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 @@ -250,14 +273,14 @@ equation_of_time(double tm) * @return The Sun's apparent elevation at the specified time as seen * from the specified position, measured in radians */ -static inline double -solar_elevation_from_time(double tm, double latitude, double longitude) +static double +solar_elevation_from_time(double tc, double td, double latitude, double longitude) { - double rc = julian_centuries_to_julian_day(tm); - rc = (rc - round(rc) - 0.5) * 1440; - rc = 720.0 - rc - equation_of_time(tm); - rc = radians(rc / 4.0 - longitude); - return elevation_from_hour_angle(latitude, solar_declination(tm), rc); + 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); } /** @@ -277,33 +300,18 @@ solar_elevation_from_time(double tm, double latitude, double longitude) double libred_solar_elevation(double latitude, double longitude, double *elevation) { - double tm; - if (julian_centuries(&tm)) + double tc, td; + if (julian_time(&tc, &td)) return -1; - *elevation = degrees(solar_elevation_from_time(tm, latitude, longitude)); + *elevation = degrees(solar_elevation_from_time(tc, td, latitude, longitude)); return 0; } /** - * Exit if time the is before year 0 in J2000 - * - * @return 0 on success, -1 on error + * This function is obsolete */ int libred_check_timetravel(void) { -#if !defined(TIMETRAVELLER) - struct timespec now; - if (clock_gettime(CLOCK_REALTIME, &now)) - return -1; - if (now.tv_sec < (time_t)946728000L) { - fprintf(stderr, - "We have detected that you are a time-traveller" - "(or your clock is not configured correctly.)" - "Please recompile libred with -DTIMETRAVELLER" - "(or correct your clock.)"); - exit(1); - } -#endif return 0; } |