/*- * SPDX-License-Identifier: BSD-3-Clause * * Copyright (c) 2020 The DragonFly Project. All rights reserved. * * This code is derived from software contributed to The DragonFly Project * by Aaron LI * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. 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. * 3. Neither the name of The DragonFly Project 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 * COPYRIGHT HOLDERS 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. * * Reference: * Calendrical Calculations, The Ultimate Edition (4th Edition) * by Edward M. Reingold and Nachum Dershowitz * 2018, Cambridge University Press */ #include #include #include "calendar.h" #include "basics.h" #include "ecclesiastical.h" #include "gregorian.h" #include "julian.h" #include "utils.h" /* * Calculate the fixed date (RD) of Orthodox Easter in Gregorian year $g_year. * Ref: Sec.(9.1), Eq.(9.1) */ int orthodox_easter(int g_year) { /* Age of moon for April 5 */ int shifted_epact = mod(14 + 11 * mod(g_year, 19), 30); /* Day after full moon on/after March 21 */ int j_year = (g_year > 0) ? g_year : (g_year - 1); struct date april19 = { j_year, 4, 19 }; int paschal_moon = fixed_from_julian(&april19) - shifted_epact; return kday_after(SUNDAY, paschal_moon); } /* * Calculate the fixed date (RD) of Gregorian Easter (used by Catholic and * Protestant churches) in Gregorian year $g_year. * Ref: Sec.(9.2), Eq.(9.3) */ int easter(int g_year) { int century = div_floor(g_year, 100) + 1; int y_mod19 = mod(g_year, 19); int n = (14 + 11 * y_mod19 - (int)floor(century * 0.75) + div_floor(5 + 8 * century, 25)); int shifted_epact = mod(n, 30); if (shifted_epact == 0 || (shifted_epact == 1 && y_mod19 > 10)) shifted_epact++; struct date april19 = { g_year, 4, 19 }; int paschal_moon = fixed_from_gregorian(&april19) - shifted_epact; return kday_after(SUNDAY, paschal_moon); } /* * Calculate the fixed date (RD) of Advent Sunday (the 4th Sunday * before Christmas, equivalent to the Sunday closest to November 30) * in Gregorian year $g_year. * Ref: Sec.(2.5), Eq.(2.42) */ int advent(int g_year) { struct date date = { g_year, 11, 30 }; int rd; if (Calendar->id == CAL_JULIAN) rd = fixed_from_julian(&date); else rd = fixed_from_gregorian(&date); return kday_nearest(SUNDAY, rd); }