chromium/third_party/icu/source/i18n/islamcal.h

// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
 ********************************************************************************
 * Copyright (C) 2003-2013, International Business Machines Corporation
 * and others. All Rights Reserved.
 ******************************************************************************
 *
 * File ISLAMCAL.H
 *
 * Modification History:
 *
 *   Date        Name        Description
 *   10/14/2003  srl         ported from java IslamicCalendar
 *****************************************************************************
 */

#ifndef ISLAMCAL_H
#define ISLAMCAL_H

#include "unicode/utypes.h"

#if !UCONFIG_NO_FORMATTING

#include "unicode/calendar.h"

U_NAMESPACE_BEGIN

/**
 * <code>IslamicCalendar</code> is a subclass of <code>Calendar</code>
 * that implements the Islamic civil and religious calendars.  It
 * is used as the civil calendar in most of the Arab world and the
 * liturgical calendar of the Islamic faith worldwide.  This calendar
 * is also known as the "Hijri" calendar, since it starts at the time
 * of Mohammed's emigration (or "hijra") to Medinah on Thursday, 
 * July 15, 622 AD (Julian).
 * <p>
 * The Islamic calendar is strictly lunar, and thus an Islamic year of twelve
 * lunar months does not correspond to the solar year used by most other
 * calendar systems, including the Gregorian.  An Islamic year is, on average,
 * about 354 days long, so each successive Islamic year starts about 11 days
 * earlier in the corresponding Gregorian year.
 * <p>
 * Each month of the calendar starts when the new moon's crescent is visible
 * at sunset.  However, in order to keep the time fields in this class
 * synchronized with those of the other calendars and with local clock time,
 * we treat days and months as beginning at midnight,
 * roughly 6 hours after the corresponding sunset.
 * <p>
 * There are two main variants of the Islamic calendar in existence.  The first
 * is the <em>civil</em> calendar, which uses a fixed cycle of alternating 29-
 * and 30-day months, with a leap day added to the last month of 11 out of
 * every 30 years.  This calendar is easily calculated and thus predictable in
 * advance, so it is used as the civil calendar in a number of Arab countries.
 * This is the default behavior of a newly-created <code>IslamicCalendar</code>
 * object. This calendar variant is implemented in the IslamicCivilCalendar
 * class.
 * <p>
 * The Islamic <em>religious</em> calendar, however, is based on the <em>observation</em>
 * of the crescent moon.  It is thus affected by the position at which the
 * observations are made, seasonal variations in the time of sunset, the
 * eccentricities of the moon's orbit, and even the weather at the observation
 * site.  This makes it impossible to calculate in advance, and it causes the
 * start of a month in the religious calendar to differ from the civil calendar
 * by up to three days.
 * <p>
 * Using astronomical calculations for the position of the sun and moon, the
 * moon's illumination, and other factors, it is possible to determine the start
 * of a lunar month with a fairly high degree of certainty.  However, these
 * calculations are extremely complicated and thus slow, so most algorithms,
 * including the one used here, are only approximations of the true astronomical
 * calculations.  At present, the approximations used in this class are fairly
 * simplistic; they will be improved in later versions of the code.
 * <p>
 *
 * @see GregorianCalendar
 *
 * @author Laura Werner
 * @author Alan Liu
 * @author Steven R. Loomis
 * @internal
 */
class U_I18N_API IslamicCalendar : public Calendar { … };

/*
 * IslamicCivilCalendar is one of the two main variants of the Islamic calendar.
 * The <em>civil</em> calendar, which uses a fixed cycle of alternating 29-
 * and 30-day months, with a leap day added to the last month of 11 out of
 * every 30 years.  This calendar is easily calculated and thus predictable in
 * advance, so it is used as the civil calendar in a number of Arab countries.
 * This calendar is referring as "Islamic calendar, tabular (intercalary years
 * [2,5,7,10,13,16,18,21,24,26,29]- civil epoch" in CLDR.
 */
class U_I18N_API IslamicCivilCalendar : public IslamicCalendar { … };

/*
 * IslamicTBLACalendar calendar.
 * This is a subclass of IslamicCivilCalendar. The only differences in the
 * calendar math is it uses different epoch.
 * This calendar is referring as "Islamic calendar, tabular (intercalary years
 * [2,5,7,10,13,16,18,21,24,26,29] - astronomical epoch" in CLDR.
 */
class U_I18N_API IslamicTBLACalendar : public IslamicCivilCalendar { … };

/*
 * IslamicUmalquraCalendar
 * This calendar is referred as "Islamic calendar, Umm al-Qura" in CLDR.
 */
class U_I18N_API IslamicUmalquraCalendar : public IslamicCalendar { … };


/*
 * IslamicRGSACalendar
 * Islamic calendar, Saudi Arabia sighting. Since the calendar depends on the
 * sighting, it is impossible to implement by algorithm ahead of time. It is
 * currently identical to IslamicCalendar except the getType will return
 * "islamic-rgsa".
 */
class U_I18N_API IslamicRGSACalendar : public IslamicCalendar { … };

U_NAMESPACE_END

#endif
#endif