Diffstat (limited to 'libical/src/libical/caldate.c') (more/less context) (ignore whitespace changes)
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diff --git a/libical/src/libical/caldate.c b/libical/src/libical/caldate.c new file mode 100644 index 0000000..f5554f6 --- a/dev/null +++ b/libical/src/libical/caldate.c @@ -0,0 +1,176 @@ +/* + * Copyright (c) 1986-2000, Hiram Clawson + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or + * without modification, are permitted provided that the following + * conditions are met: + * + * Redistributions of source code must retain the above + * copyright notice, this list of conditions and the + * following disclaimer. + * + * Redistributions in binary form must reproduce the + * above copyright notice, this list of conditions and + * the following disclaimer in the documentation and/or + * other materials provided with the distribution. + * + * Neither name of The Museum of Hiram nor the names of + * its contributors may be used to endorse or promote products + * derived from this software without specific prior + * written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND + * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, + * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. + * IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, + * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES + * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, + * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING + * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF + * THE POSSIBILITY OF SUCH DAMAGE. + */ + +#include "astime.h" /* time structures */ + +/** + * caldat computes the day of the week, the day of the year + * the gregorian (or julian) calendar date and the universal + * time from the julian decimal date. + * for astronomical purposes, The Gregorian calendar reform occurred + * on 15 Oct. 1582. This is 05 Oct 1582 by the julian calendar. + + * Input: a ut_instant structure pointer, where the j_date element + * has been set. ( = 0 for 01 Jan 4713 B.C. 12 HR UT ) + * + * output: will set all the other elements of the structure. + * As a convienence, the function will also return the year. + * + * Reference: Astronomial formulae for calculators, meeus, p 23 + * from fortran program by F. Espenak - April 1982 Page 277, + * 50 Year canon of solar eclipses: 1986-2035 + * + */ + +long caldat( date ) +struct ut_instant * date; +{ + double frac; + long jd; + long ka; + long kb; + long kc; + long kd; + long ke; + long ialp; + + jd = (long) (date->j_date + 0.5); /* integer julian date */ + frac = date->j_date + 0.5 - (double) jd + 1.0e-10; /* day fraction */ + ka = (long) jd; + if ( jd >= 2299161L ) + { + ialp = ( (double) jd - 1867216.25 ) / ( 36524.25 ); + ka = jd + 1L + ialp - ( ialp >> 2 ); + } + kb = ka + 1524L; + kc = ( (double) kb - 122.1 ) / 365.25; + kd = (double) kc * 365.25; + ke = (double) ( kb - kd ) / 30.6001; + date->day = kb - kd - ((long) ( (double) ke * 30.6001 )); + if ( ke > 13L ) + date->month = ke - 13L; + else + date->month = ke - 1L; + if ( (date->month == 2) && (date->day > 28) ) + date->day = 29; + if ( (date->month == 2) && (date->day == 29) && (ke == 3L) ) + date->year = kc - 4716L; + else if ( date->month > 2 ) + date->year = kc - 4716L; + else + date->year = kc - 4715L; + date->i_hour = date->d_hour = frac * 24.0; /* hour */ + date->i_minute = date->d_minute = + ( date->d_hour - (double) date->i_hour ) * 60.0; /* minute */ + date->i_second = date->d_second = + ( date->d_minute - (double) date->i_minute ) * 60.0;/* second */ + date->weekday = (jd + 1L) % 7L; /* day of week */ + if ( date->year == ((date->year >> 2) << 2) ) + date->day_of_year = + ( ( 275 * date->month ) / 9) + - ((date->month + 9) / 12) + + date->day - 30; + else + date->day_of_year = + ( ( 275 * date->month ) / 9) + - (((date->month + 9) / 12) << 1) + + date->day - 30; + return( date->year ); +} + +/** + * juldat computes the julian decimal date (j_date) from + * the gregorian (or Julian) calendar date. + * for astronomical purposes, The Gregorian calendar reform occurred + * on 15 Oct. 1582. This is 05 Oct 1582 by the julian calendar. + * Input: a ut_instant structure pointer where Day, Month, Year and + * i_hour, i_minute, d_second have been set for the date + * in question. + * + * Output: the j_date and weekday elements of the structure will be set. + * Also, the return value of the function will be the j_date too. + * + * Reference: Astronomial formulae for calculators, meeus, p 23 + * from fortran program by F. Espenak - April 1982 Page 276, + * 50 Year canon of solar eclipses: 1986-2035 + */ + +double juldat( date ) +struct ut_instant * date; +{ + double frac, gyr; + long iy0, im0; + long ia, ib; + long jd; + + /* decimal day fraction */ + frac = (( double)date->i_hour/ 24.0) + + ((double) date->i_minute / 1440.0) + + (date->d_second / 86400.0); + /* convert date to format YYYY.MMDDdd */ + gyr = (double) date->year + + (0.01 * (double) date->month) + + (0.0001 * (double) date->day) + + (0.0001 * frac) + 1.0e-9; + /* conversion factors */ + if ( date->month <= 2 ) + { + iy0 = date->year - 1L; + im0 = date->month + 12; + } + else + { + iy0 = date->year; + im0 = date->month; + } + ia = iy0 / 100L; + ib = 2L - ia + (ia >> 2); + /* calculate julian date */ + if ( date->year < 0L ) + jd = (long) ((365.25 * (double) iy0) - 0.75) + + (long) (30.6001 * (im0 + 1L) ) + + (long) date->day + 1720994L; + else + jd = (long) (365.25 * (double) iy0) + + (long) (30.6001 * (double) (im0 + 1L)) + + (long) date->day + 1720994L; + if ( gyr >= 1582.1015 ) /* on or after 15 October 1582 */ + jd += ib; + date->j_date = (double) jd + frac + 0.5; + jd = (long) (date->j_date + 0.5); + date->weekday = (jd + 1L) % 7L; + return( date->j_date ); +} /* end of double juldat( date ) */ |