AbsoluteDate.java

  1. /* Copyright 2002-2019 CS Systèmes d'Information
  2.  * Licensed to CS Systèmes d'Information (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.time;

  19. import java.io.Serializable;
  20. import java.util.Date;
  21. import java.util.TimeZone;

  23. import org.hipparchus.util.FastMath;
  24. import org.hipparchus.util.MathArrays;
  25. import org.orekit.errors.OrekitException;
  26. import org.orekit.errors.OrekitIllegalArgumentException;
  27. import org.orekit.errors.OrekitMessages;
  28. import org.orekit.utils.Constants;


  31. /** This class represents a specific instant in time.

  33.  * <p>Instances of this class are considered to be absolute in the sense
  34.  * that each one represent the occurrence of some event and can be compared
  35.  * to other instances or located in <em>any</em> {@link TimeScale time scale}. In
  36.  * other words the different locations of an event with respect to two different
  37.  * time scales (say {@link TAIScale TAI} and {@link UTCScale UTC} for example) are
  38.  * simply different perspective related to a single object. Only one
  39.  * <code>AbsoluteDate</code> instance is needed, both representations being available
  40.  * from this single instance by specifying the time scales as parameter when calling
  41.  * the ad-hoc methods.</p>
  42.  *
  43.  * <p>Since an instance is not bound to a specific time-scale, all methods related
  44.  * to the location of the date within some time scale require to provide the time
  45.  * scale as an argument. It is therefore possible to define a date in one time scale
  46.  * and to use it in another one. An example of such use is to read a date from a file
  47.  * in UTC and write it in another file in TAI. This can be done as follows:</p>
  48.  * <pre>
  49.  *   DateTimeComponents utcComponents = readNextDate();
  50.  *   AbsoluteDate date = new AbsoluteDate(utcComponents, TimeScalesFactory.getUTC());
  51.  *   writeNextDate(date.getComponents(TimeScalesFactory.getTAI()));
  52.  * </pre>
  53.  *
  54.  * <p>Two complementary views are available:</p>
  55.  * <ul>
  56.  *   <li><p>location view (mainly for input/output or conversions)</p>
  57.  *   <p>locations represent the coordinate of one event with respect to a
  58.  *   {@link TimeScale time scale}. The related methods are {@link
  59.  *   #AbsoluteDate(DateComponents, TimeComponents, TimeScale)}, {@link
  60.  *   #AbsoluteDate(int, int, int, int, int, double, TimeScale)}, {@link
  61.  *   #AbsoluteDate(int, int, int, TimeScale)}, {@link #AbsoluteDate(Date,
  62.  *   TimeScale)}, {@link #createGPSDate(int, double)}, {@link
  63.  *   #parseCCSDSCalendarSegmentedTimeCode(byte, byte[])}, toString(){@link
  64.  *   #toDate(TimeScale)}, {@link #toString(TimeScale) toString(timeScale)},
  65.  *   {@link #toString()}, and {@link #timeScalesOffset}.</p>
  66.  *   </li>
  67.  *   <li><p>offset view (mainly for physical computation)</p>
  68.  *   <p>offsets represent either the flow of time between two events
  69.  *   (two instances of the class) or durations. They are counted in seconds,
  70.  *   are continuous and could be measured using only a virtually perfect stopwatch.
  71.  *   The related methods are {@link #AbsoluteDate(AbsoluteDate, double)},
  72.  *   {@link #parseCCSDSUnsegmentedTimeCode(byte, byte, byte[], AbsoluteDate)},
  73.  *   {@link #parseCCSDSDaySegmentedTimeCode(byte, byte[], DateComponents)},
  74.  *   {@link #durationFrom(AbsoluteDate)}, {@link #compareTo(AbsoluteDate)}, {@link #equals(Object)}
  75.  *   and {@link #hashCode()}.</p>
  76.  *   </li>
  77.  * </ul>
  78.  * <p>
  79.  * A few reference epochs which are commonly used in space systems have been defined. These
  80.  * epochs can be used as the basis for offset computation. The supported epochs are:
  81.  * {@link #JULIAN_EPOCH}, {@link #MODIFIED_JULIAN_EPOCH}, {@link #FIFTIES_EPOCH},
  82.  * {@link #CCSDS_EPOCH}, {@link #GALILEO_EPOCH}, {@link #GPS_EPOCH}, {@link #J2000_EPOCH},
  83.  * {@link #JAVA_EPOCH}. There are also two factory methods {@link #createJulianEpoch(double)}
  84.  * and {@link #createBesselianEpoch(double)} that can be used to compute other reference
  85.  * epochs like J1900.0 or B1950.0.
  86.  * In addition to these reference epochs, two other constants are defined for convenience:
  87.  * {@link #PAST_INFINITY} and {@link #FUTURE_INFINITY}, which can be used either as dummy
  88.  * dates when a date is not yet initialized, or for initialization of loops searching for
  89.  * a min or max date.
  90.  * </p>
  91.  * <p>
  92.  * Instances of the <code>AbsoluteDate</code> class are guaranteed to be immutable.
  93.  * </p>
  94.  * @author Luc Maisonobe
  95.  * @see TimeScale
  96.  * @see TimeStamped
  97.  * @see ChronologicalComparator
  98.  */
  99. public class AbsoluteDate
  100.     implements TimeStamped, TimeShiftable<AbsoluteDate>, Comparable<AbsoluteDate>, Serializable {

  102.     /** Reference epoch for julian dates: -4712-01-01T12:00:00 Terrestrial Time.
  103.      * <p>Both <code>java.util.Date</code> and {@link DateComponents} classes
  104.      * follow the astronomical conventions and consider a year 0 between
  105.      * years -1 and +1, hence this reference date lies in year -4712 and not
  106.      * in year -4713 as can be seen in other documents or programs that obey
  107.      * a different convention (for example the <code>convcal</code> utility).</p>
  108.      */
  109.     public static final AbsoluteDate JULIAN_EPOCH =
  110.         new AbsoluteDate(DateComponents.JULIAN_EPOCH, TimeComponents.H12, TimeScalesFactory.getTT());

  112.     /** Reference epoch for modified julian dates: 1858-11-17T00:00:00 Terrestrial Time. */
  113.     public static final AbsoluteDate MODIFIED_JULIAN_EPOCH =
  114.         new AbsoluteDate(DateComponents.MODIFIED_JULIAN_EPOCH, TimeComponents.H00, TimeScalesFactory.getTT());

  116.     /** Reference epoch for 1950 dates: 1950-01-01T00:00:00 Terrestrial Time. */
  117.     public static final AbsoluteDate FIFTIES_EPOCH =
  118.         new AbsoluteDate(DateComponents.FIFTIES_EPOCH, TimeComponents.H00, TimeScalesFactory.getTT());

  120.     /** Reference epoch for CCSDS Time Code Format (CCSDS 301.0-B-4):
  121.      * 1958-01-01T00:00:00 International Atomic Time (<em>not</em> UTC). */
  122.     public static final AbsoluteDate CCSDS_EPOCH =
  123.         new AbsoluteDate(DateComponents.CCSDS_EPOCH, TimeComponents.H00, TimeScalesFactory.getTAI());

  125.     /** Reference epoch for Galileo System Time: 1999-08-22T00:00:00 UTC. */
  126.     public static final AbsoluteDate GALILEO_EPOCH =
  127.         new AbsoluteDate(DateComponents.GALILEO_EPOCH, new TimeComponents(0, 0, 32),
  128.                          TimeScalesFactory.getTAI());

  130.     /** Reference epoch for GPS weeks: 1980-01-06T00:00:00 GPS time. */
  131.     public static final AbsoluteDate GPS_EPOCH =
  132.         new AbsoluteDate(DateComponents.GPS_EPOCH, TimeComponents.H00, TimeScalesFactory.getGPS());

  134.     /** J2000.0 Reference epoch: 2000-01-01T12:00:00 Terrestrial Time (<em>not</em> UTC).
  135.      * @see #createJulianEpoch(double)
  136.      * @see #createBesselianEpoch(double)
  137.      */
  138.     public static final AbsoluteDate J2000_EPOCH =
  139.         new AbsoluteDate(DateComponents.J2000_EPOCH, TimeComponents.H12, TimeScalesFactory.getTT());

  141.     /** Java Reference epoch: 1970-01-01T00:00:00 Universal Time Coordinate.
  142.      * <p>
  143.      * Between 1968-02-01 and 1972-01-01, UTC-TAI = 4.213 170 0s + (MJD - 39 126) x 0.002 592s.
  144.      * As on 1970-01-01 MJD = 40587, UTC-TAI = 8.000082s
  145.      * </p>
  146.      */
  147.     public static final AbsoluteDate JAVA_EPOCH =
  148.         new AbsoluteDate(DateComponents.JAVA_EPOCH, TimeScalesFactory.getTAI()).shiftedBy(8.000082);

  150.     /** Dummy date at infinity in the past direction. */
  151.     public static final AbsoluteDate PAST_INFINITY = JAVA_EPOCH.shiftedBy(Double.NEGATIVE_INFINITY);

  153.     /** Dummy date at infinity in the future direction. */
  154.     public static final AbsoluteDate FUTURE_INFINITY = JAVA_EPOCH.shiftedBy(Double.POSITIVE_INFINITY);

  156.     /** Serializable UID. */
  157.     private static final long serialVersionUID = 617061803741806846L;

  159.     /** Reference epoch in seconds from 2000-01-01T12:00:00 TAI.
  160.      * <p>Beware, it is not {@link #J2000_EPOCH} since it is in TAI and not in TT.</p> */
  161.     private final long epoch;

  163.     /** Offset from the reference epoch in seconds. */
  164.     private final double offset;

  166.     /** Create an instance with a default value ({@link #J2000_EPOCH}).
  167.      */
  168.     public AbsoluteDate() {
  169.         epoch  = J2000_EPOCH.epoch;
  170.         offset = J2000_EPOCH.offset;
  171.     }

  173.     /** Build an instance from a location (parsed from a string) in a {@link TimeScale time scale}.
  174.      * <p>
  175.      * The supported formats for location are mainly the ones defined in ISO-8601 standard,
  176.      * the exact subset is explained in {@link DateTimeComponents#parseDateTime(String)},
  177.      * {@link DateComponents#parseDate(String)} and {@link TimeComponents#parseTime(String)}.
  178.      * </p>
  179.      * <p>
  180.      * As CCSDS ASCII calendar segmented time code is a trimmed down version of ISO-8601,
  181.      * it is also supported by this constructor.
  182.      * </p>
  183.      * @param location location in the time scale, must be in a supported format
  184.      * @param timeScale time scale
  185.      * @exception IllegalArgumentException if location string is not in a supported format
  186.      */
  187.     public AbsoluteDate(final String location, final TimeScale timeScale) {
  188.         this(DateTimeComponents.parseDateTime(location), timeScale);
  189.     }

  191.     /** Build an instance from a location in a {@link TimeScale time scale}.
  192.      * @param location location in the time scale
  193.      * @param timeScale time scale
  194.      */
  195.     public AbsoluteDate(final DateTimeComponents location, final TimeScale timeScale) {
  196.         this(location.getDate(), location.getTime(), timeScale);
  197.     }

  199.     /** Build an instance from a location in a {@link TimeScale time scale}.
  200.      * @param date date location in the time scale
  201.      * @param time time location in the time scale
  202.      * @param timeScale time scale
  203.      */
  204.     public AbsoluteDate(final DateComponents date, final TimeComponents time,
  205.                         final TimeScale timeScale) {

  207.         final double seconds  = time.getSecond();
  208.         final double tsOffset = timeScale.offsetToTAI(date, time);

  210.         // compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
  211.         // the following statements must NOT be simplified, they rely on floating point
  212.         // arithmetic properties (rounding and representable numbers)
  213.         // at the end, the EXACT result of addition seconds + tsOffset
  214.         // is sum + residual, where sum is the closest representable number to the exact
  215.         // result and residual is the missing part that does not fit in the first number
  216.         final double sum      = seconds + tsOffset;
  217.         final double sPrime   = sum - tsOffset;
  218.         final double tPrime   = sum - sPrime;
  219.         final double deltaS   = seconds  - sPrime;
  220.         final double deltaT   = tsOffset - tPrime;
  221.         final double residual = deltaS   + deltaT;
  222.         final long   dl       = (long) FastMath.floor(sum);

  224.         offset = (sum - dl) + residual;
  225.         epoch  = 60l * ((date.getJ2000Day() * 24l + time.getHour()) * 60l +
  226.                         time.getMinute() - time.getMinutesFromUTC() - 720l) + dl;

  228.     }

  230.     /** Build an instance from a location in a {@link TimeScale time scale}.
  231.      * @param year year number (may be 0 or negative for BC years)
  232.      * @param month month number from 1 to 12
  233.      * @param day day number from 1 to 31
  234.      * @param hour hour number from 0 to 23
  235.      * @param minute minute number from 0 to 59
  236.      * @param second second number from 0.0 to 60.0 (excluded)
  237.      * @param timeScale time scale
  238.      * @exception IllegalArgumentException if inconsistent arguments
  239.      * are given (parameters out of range)
  240.      */
  241.     public AbsoluteDate(final int year, final int month, final int day,
  242.                         final int hour, final int minute, final double second,
  243.                         final TimeScale timeScale) throws IllegalArgumentException {
  244.         this(new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
  245.     }

  247.     /** Build an instance from a location in a {@link TimeScale time scale}.
  248.      * @param year year number (may be 0 or negative for BC years)
  249.      * @param month month enumerate
  250.      * @param day day number from 1 to 31
  251.      * @param hour hour number from 0 to 23
  252.      * @param minute minute number from 0 to 59
  253.      * @param second second number from 0.0 to 60.0 (excluded)
  254.      * @param timeScale time scale
  255.      * @exception IllegalArgumentException if inconsistent arguments
  256.      * are given (parameters out of range)
  257.      */
  258.     public AbsoluteDate(final int year, final Month month, final int day,
  259.                         final int hour, final int minute, final double second,
  260.                         final TimeScale timeScale) throws IllegalArgumentException {
  261.         this(new DateComponents(year, month, day), new TimeComponents(hour, minute, second), timeScale);
  262.     }

  264.     /** Build an instance from a location in a {@link TimeScale time scale}.
  265.      * <p>The hour is set to 00:00:00.000.</p>
  266.      * @param date date location in the time scale
  267.      * @param timeScale time scale
  268.      * @exception IllegalArgumentException if inconsistent arguments
  269.      * are given (parameters out of range)
  270.      */
  271.     public AbsoluteDate(final DateComponents date, final TimeScale timeScale)
  272.         throws IllegalArgumentException {
  273.         this(date, TimeComponents.H00, timeScale);
  274.     }

  276.     /** Build an instance from a location in a {@link TimeScale time scale}.
  277.      * <p>The hour is set to 00:00:00.000.</p>
  278.      * @param year year number (may be 0 or negative for BC years)
  279.      * @param month month number from 1 to 12
  280.      * @param day day number from 1 to 31
  281.      * @param timeScale time scale
  282.      * @exception IllegalArgumentException if inconsistent arguments
  283.      * are given (parameters out of range)
  284.      */
  285.     public AbsoluteDate(final int year, final int month, final int day,
  286.                         final TimeScale timeScale) throws IllegalArgumentException {
  287.         this(new DateComponents(year, month, day), TimeComponents.H00, timeScale);
  288.     }

  290.     /** Build an instance from a location in a {@link TimeScale time scale}.
  291.      * <p>The hour is set to 00:00:00.000.</p>
  292.      * @param year year number (may be 0 or negative for BC years)
  293.      * @param month month enumerate
  294.      * @param day day number from 1 to 31
  295.      * @param timeScale time scale
  296.      * @exception IllegalArgumentException if inconsistent arguments
  297.      * are given (parameters out of range)
  298.      */
  299.     public AbsoluteDate(final int year, final Month month, final int day,
  300.                         final TimeScale timeScale) throws IllegalArgumentException {
  301.         this(new DateComponents(year, month, day), TimeComponents.H00, timeScale);
  302.     }

  304.     /** Build an instance from a location in a {@link TimeScale time scale}.
  305.      * @param location location in the time scale
  306.      * @param timeScale time scale
  307.      */
  308.     public AbsoluteDate(final Date location, final TimeScale timeScale) {
  309.         this(new DateComponents(DateComponents.JAVA_EPOCH,
  310.                                 (int) (location.getTime() / 86400000l)),
  311.                                 new TimeComponents(0.001 * (location.getTime() % 86400000l)),
  312.              timeScale);
  313.     }

  315.     /** Build an instance from an elapsed duration since to another instant.
  316.      * <p>It is important to note that the elapsed duration is <em>not</em>
  317.      * the difference between two readings on a time scale. As an example,
  318.      * the duration between the two instants leading to the readings
  319.      * 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the {@link UTCScale UTC}
  320.      * time scale is <em>not</em> 1 second, but a stop watch would have measured
  321.      * an elapsed duration of 2 seconds between these two instances because a leap
  322.      * second was introduced at the end of 2005 in this time scale.</p>
  323.      * <p>This constructor is the reverse of the {@link #durationFrom(AbsoluteDate)}
  324.      * method.</p>
  325.      * @param since start instant of the measured duration
  326.      * @param elapsedDuration physically elapsed duration from the <code>since</code>
  327.      * instant, as measured in a regular time scale
  328.      * @see #durationFrom(AbsoluteDate)
  329.      */
  330.     public AbsoluteDate(final AbsoluteDate since, final double elapsedDuration) {

  332.         final double sum = since.offset + elapsedDuration;
  333.         if (Double.isInfinite(sum)) {
  334.             offset = sum;
  335.             epoch  = (sum < 0) ? Long.MIN_VALUE : Long.MAX_VALUE;
  336.         } else {
  337.             // compute sum exactly, using Møller-Knuth TwoSum algorithm without branching
  338.             // the following statements must NOT be simplified, they rely on floating point
  339.             // arithmetic properties (rounding and representable numbers)
  340.             // at the end, the EXACT result of addition since.offset + elapsedDuration
  341.             // is sum + residual, where sum is the closest representable number to the exact
  342.             // result and residual is the missing part that does not fit in the first number
  343.             final double oPrime   = sum - elapsedDuration;
  344.             final double dPrime   = sum - oPrime;
  345.             final double deltaO   = since.offset - oPrime;
  346.             final double deltaD   = elapsedDuration - dPrime;
  347.             final double residual = deltaO + deltaD;
  348.             final long   dl       = (long) FastMath.floor(sum);
  349.             offset = (sum - dl) + residual;
  350.             epoch  = since.epoch  + dl;
  351.         }
  352.     }

  354.     /** Build an instance from an apparent clock offset with respect to another
  355.      * instant <em>in the perspective of a specific {@link TimeScale time scale}</em>.
  356.      * <p>It is important to note that the apparent clock offset <em>is</em> the
  357.      * difference between two readings on a time scale and <em>not</em> an elapsed
  358.      * duration. As an example, the apparent clock offset between the two instants
  359.      * leading to the readings 2005-12-31T23:59:59 and 2006-01-01T00:00:00 in the
  360.      * {@link UTCScale UTC} time scale is 1 second, but the elapsed duration is 2
  361.      * seconds because a leap second has been introduced at the end of 2005 in this
  362.      * time scale.</p>
  363.      * <p>This constructor is the reverse of the {@link #offsetFrom(AbsoluteDate,
  364.      * TimeScale)} method.</p>
  365.      * @param reference reference instant
  366.      * @param apparentOffset apparent clock offset from the reference instant
  367.      * (difference between two readings in the specified time scale)
  368.      * @param timeScale time scale with respect to which the offset is defined
  369.      * @see #offsetFrom(AbsoluteDate, TimeScale)
  370.      */
  371.     public AbsoluteDate(final AbsoluteDate reference, final double apparentOffset,
  372.                         final TimeScale timeScale) {
  373.         this(new DateTimeComponents(reference.getComponents(timeScale), apparentOffset),
  374.              timeScale);
  375.     }

  377.     /** Build a date from its internal components.
  378.      * <p>
  379.      * This method is reserved for internal used (for example by {@link FieldAbsoluteDate}).
  380.      * </p>
  381.      * @param epoch reference epoch in seconds from 2000-01-01T12:00:00 TAI.
  382.      * (beware, it is not {@link #J2000_EPOCH} since it is in TAI and not in TT)
  383.      * @param offset offset from the reference epoch in seconds (must be
  384.      * between 0.0 included and 1.0 excluded)
  385.      * @since 9.0
  386.      */
  387.     AbsoluteDate(final long epoch, final double offset) {
  388.         this.epoch  = epoch;
  389.         this.offset = offset;
  390.     }

  392.     /** Get the reference epoch in seconds from 2000-01-01T12:00:00 TAI.
  393.      * <p>
  394.      * This method is reserved for internal used (for example by {@link FieldAbsoluteDate}).
  395.      * </p>
  396.      * <p>
  397.      * Beware, it is not {@link #J2000_EPOCH} since it is in TAI and not in TT.
  398.      * </p>
  399.      * @return reference epoch in seconds from 2000-01-01T12:00:00 TAI
  400.      * @since 9.0
  401.      */
  402.     long getEpoch() {
  403.         return epoch;
  404.     }

  406.     /** Get the offset from the reference epoch in seconds.
  407.      * <p>
  408.      * This method is reserved for internal used (for example by {@link FieldAbsoluteDate}).
  409.      * </p>
  410.      * @return offset from the reference epoch in seconds
  411.      * @since 9.0
  412.      */
  413.     double getOffset() {
  414.         return offset;
  415.     }

  417.     /** Build an instance from a CCSDS Unsegmented Time Code (CUC).
  418.      * <p>
  419.      * CCSDS Unsegmented Time Code is defined in the blue book:
  420.      * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
  421.      * </p>
  422.      * <p>
  423.      * If the date to be parsed is formatted using version 3 of the standard
  424.      * (CCSDS 301.0-B-3 published in 2002) or if the extension of the preamble
  425.      * field introduced in version 4 of the standard is not used, then the
  426.      * {@code preambleField2} parameter can be set to 0.
  427.      * </p>
  428.      * @param preambleField1 first byte of the field specifying the format, often
  429.      * not transmitted in data interfaces, as it is constant for a given data interface
  430.      * @param preambleField2 second byte of the field specifying the format
  431.      * (added in revision 4 of the CCSDS standard in 2010), often not transmitted in data
  432.      * interfaces, as it is constant for a given data interface (value ignored if presence
  433.      * not signaled in {@code preambleField1})
  434.      * @param timeField byte array containing the time code
  435.      * @param agencyDefinedEpoch reference epoch, ignored if the preamble field
  436.      * specifies the {@link #CCSDS_EPOCH CCSDS reference epoch} is used (and hence
  437.      * may be null in this case)
  438.      * @return an instance corresponding to the specified date
  439.      */
  440.     public static AbsoluteDate parseCCSDSUnsegmentedTimeCode(final byte preambleField1,
  441.                                                              final byte preambleField2,
  442.                                                              final byte[] timeField,
  443.                                                              final AbsoluteDate agencyDefinedEpoch) {

  445.         // time code identification and reference epoch
  446.         final AbsoluteDate epoch;
  447.         switch (preambleField1 & 0x70) {
  448.             case 0x10:
  449.                 // the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
  450.                 epoch = CCSDS_EPOCH;
  451.                 break;
  452.             case 0x20:
  453.                 // the reference epoch is agency defined
  454.                 if (agencyDefinedEpoch == null) {
  455.                     throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
  456.                 }
  457.                 epoch = agencyDefinedEpoch;
  458.                 break;
  459.             default :
  460.                 throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  461.                                           formatByte(preambleField1));
  462.         }

  464.         // time field lengths
  465.         int coarseTimeLength = 1 + ((preambleField1 & 0x0C) >>> 2);
  466.         int fineTimeLength   = preambleField1 & 0x03;

  468.         if ((preambleField1 & 0x80) != 0x0) {
  469.             // there is an additional octet in preamble field
  470.             coarseTimeLength += (preambleField2 & 0x60) >>> 5;
  471.             fineTimeLength   += (preambleField2 & 0x1C) >>> 2;
  472.         }

  474.         if (timeField.length != coarseTimeLength + fineTimeLength) {
  475.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
  476.                                       timeField.length, coarseTimeLength + fineTimeLength);
  477.         }

  479.         double seconds = 0;
  480.         for (int i = 0; i < coarseTimeLength; ++i) {
  481.             seconds = seconds * 256 + toUnsigned(timeField[i]);
  482.         }
  483.         double subseconds = 0;
  484.         for (int i = timeField.length - 1; i >= coarseTimeLength; --i) {
  485.             subseconds = (subseconds + toUnsigned(timeField[i])) / 256;
  486.         }

  488.         return new AbsoluteDate(epoch, seconds).shiftedBy(subseconds);

  490.     }

  492.     /** Build an instance from a CCSDS Day Segmented Time Code (CDS).
  493.      * <p>
  494.      * CCSDS Day Segmented Time Code is defined in the blue book:
  495.      * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
  496.      * </p>
  497.      * @param preambleField field specifying the format, often not transmitted in
  498.      * data interfaces, as it is constant for a given data interface
  499.      * @param timeField byte array containing the time code
  500.      * @param agencyDefinedEpoch reference epoch, ignored if the preamble field
  501.      * specifies the {@link #CCSDS_EPOCH CCSDS reference epoch} is used (and hence
  502.      * may be null in this case)
  503.      * @return an instance corresponding to the specified date
  504.      */
  505.     public static AbsoluteDate parseCCSDSDaySegmentedTimeCode(final byte preambleField, final byte[] timeField,
  506.                                                               final DateComponents agencyDefinedEpoch) {

  508.         // time code identification
  509.         if ((preambleField & 0xF0) != 0x40) {
  510.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  511.                                       formatByte(preambleField));
  512.         }

  514.         // reference epoch
  515.         final DateComponents epoch;
  516.         if ((preambleField & 0x08) == 0x00) {
  517.             // the reference epoch is CCSDS epoch 1958-01-01T00:00:00 TAI
  518.             epoch = DateComponents.CCSDS_EPOCH;
  519.         } else {
  520.             // the reference epoch is agency defined
  521.             if (agencyDefinedEpoch == null) {
  522.                 throw new OrekitException(OrekitMessages.CCSDS_DATE_MISSING_AGENCY_EPOCH);
  523.             }
  524.             epoch = agencyDefinedEpoch;
  525.         }

  527.         // time field lengths
  528.         final int daySegmentLength = ((preambleField & 0x04) == 0x0) ? 2 : 3;
  529.         final int subMillisecondLength = (preambleField & 0x03) << 1;
  530.         if (subMillisecondLength == 6) {
  531.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  532.                                       formatByte(preambleField));
  533.         }
  534.         if (timeField.length != daySegmentLength + 4 + subMillisecondLength) {
  535.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
  536.                                       timeField.length, daySegmentLength + 4 + subMillisecondLength);
  537.         }


  540.         int i   = 0;
  541.         int day = 0;
  542.         while (i < daySegmentLength) {
  543.             day = day * 256 + toUnsigned(timeField[i++]);
  544.         }

  546.         long milliInDay = 0l;
  547.         while (i < daySegmentLength + 4) {
  548.             milliInDay = milliInDay * 256 + toUnsigned(timeField[i++]);
  549.         }
  550.         final int milli   = (int) (milliInDay % 1000l);
  551.         final int seconds = (int) ((milliInDay - milli) / 1000l);

  553.         double subMilli = 0;
  554.         double divisor  = 1;
  555.         while (i < timeField.length) {
  556.             subMilli = subMilli * 256 + toUnsigned(timeField[i++]);
  557.             divisor *= 1000;
  558.         }

  560.         final DateComponents date = new DateComponents(epoch, day);
  561.         final TimeComponents time = new TimeComponents(seconds);
  562.         return new AbsoluteDate(date, time, TimeScalesFactory.getUTC()).shiftedBy(milli * 1.0e-3 + subMilli / divisor);

  564.     }

  566.     /** Build an instance from a CCSDS Calendar Segmented Time Code (CCS).
  567.      * <p>
  568.      * CCSDS Calendar Segmented Time Code is defined in the blue book:
  569.      * CCSDS Time Code Format (CCSDS 301.0-B-4) published in November 2010
  570.      * </p>
  571.      * @param preambleField field specifying the format, often not transmitted in
  572.      * data interfaces, as it is constant for a given data interface
  573.      * @param timeField byte array containing the time code
  574.      * @return an instance corresponding to the specified date
  575.      */
  576.     public static AbsoluteDate parseCCSDSCalendarSegmentedTimeCode(final byte preambleField, final byte[] timeField) {

  578.         // time code identification
  579.         if ((preambleField & 0xF0) != 0x50) {
  580.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  581.                                       formatByte(preambleField));
  582.         }

  584.         // time field length
  585.         final int length = 7 + (preambleField & 0x07);
  586.         if (length == 14) {
  587.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_PREAMBLE_FIELD,
  588.                                       formatByte(preambleField));
  589.         }
  590.         if (timeField.length != length) {
  591.             throw new OrekitException(OrekitMessages.CCSDS_DATE_INVALID_LENGTH_TIME_FIELD,
  592.                                       timeField.length, length);
  593.         }

  595.         // date part in the first four bytes
  596.         final DateComponents date;
  597.         if ((preambleField & 0x08) == 0x00) {
  598.             // month of year and day of month variation
  599.             date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
  600.                                       toUnsigned(timeField[2]),
  601.                                       toUnsigned(timeField[3]));
  602.         } else {
  603.             // day of year variation
  604.             date = new DateComponents(toUnsigned(timeField[0]) * 256 + toUnsigned(timeField[1]),
  605.                                       toUnsigned(timeField[2]) * 256 + toUnsigned(timeField[3]));
  606.         }

  608.         // time part from bytes 5 to last (between 7 and 13 depending on precision)
  609.         final TimeComponents time = new TimeComponents(toUnsigned(timeField[4]),
  610.                                                        toUnsigned(timeField[5]),
  611.                                                        toUnsigned(timeField[6]));
  612.         double subSecond = 0;
  613.         double divisor   = 1;
  614.         for (int i = 7; i < length; ++i) {
  615.             subSecond = subSecond * 100 + toUnsigned(timeField[i]);
  616.             divisor *= 100;
  617.         }

  619.         return new AbsoluteDate(date, time, TimeScalesFactory.getUTC()).shiftedBy(subSecond / divisor);

  621.     }

  623.     /** Decode a signed byte as an unsigned int value.
  624.      * @param b byte to decode
  625.      * @return an unsigned int value
  626.      */
  627.     private static int toUnsigned(final byte b) {
  628.         final int i = (int) b;
  629.         return (i < 0) ? 256 + i : i;
  630.     }

  632.     /** Format a byte as an hex string for error messages.
  633.      * @param data byte to format
  634.      * @return a formatted string
  635.      */
  636.     private static String formatByte(final byte data) {
  637.         return "0x" + Integer.toHexString(data).toUpperCase();
  638.     }

  640.     /** Build an instance corresponding to a Julian Day date.
  641.      * @param jd Julian day
  642.      * @param secondsSinceNoon seconds in the Julian day
  643.      * (BEWARE, Julian days start at noon, so 0.0 is noon)
  644.      * @param timeScale time scale in which the seconds in day are defined
  645.      * @return a new instant
  646.      */
  647.     public static AbsoluteDate createJDDate(final int jd, final double secondsSinceNoon,
  648.                                              final TimeScale timeScale) {
  649.         return new AbsoluteDate(new DateComponents(DateComponents.JULIAN_EPOCH, jd),
  650.                                 TimeComponents.H12, timeScale).shiftedBy(secondsSinceNoon);
  651.     }

  653.     /** Build an instance corresponding to a Modified Julian Day date.
  654.      * @param mjd modified Julian day
  655.      * @param secondsInDay seconds in the day
  656.      * @param timeScale time scale in which the seconds in day are defined
  657.      * @return a new instant
  658.      * @exception OrekitIllegalArgumentException if seconds number is out of range
  659.      */
  660.     public static AbsoluteDate createMJDDate(final int mjd, final double secondsInDay,
  661.                                              final TimeScale timeScale)
  662.         throws OrekitIllegalArgumentException {
  663.         final DateComponents dc = new DateComponents(DateComponents.MODIFIED_JULIAN_EPOCH, mjd);
  664.         final TimeComponents tc;
  665.         if (secondsInDay >= Constants.JULIAN_DAY) {
  666.             // check we are really allowed to use this number of seconds
  667.             final int    secondsA = 86399; // 23:59:59, i.e. 59s in the last minute of the day
  668.             final double secondsB = secondsInDay - secondsA;
  669.             final TimeComponents safeTC = new TimeComponents(secondsA, 0.0);
  670.             final AbsoluteDate safeDate = new AbsoluteDate(dc, safeTC, timeScale);
  671.             if (timeScale.minuteDuration(safeDate) > 59 + secondsB) {
  672.                 // we are within the last minute of the day, the number of seconds is OK
  673.                 return safeDate.shiftedBy(secondsB);
  674.             } else {
  675.                 // let TimeComponents trigger an OrekitIllegalArgumentException
  676.                 // for the wrong number of seconds
  677.                 tc = new TimeComponents(secondsA, secondsB);
  678.             }
  679.         } else {
  680.             tc = new TimeComponents(secondsInDay);
  681.         }

  683.         // create the date
  684.         return new AbsoluteDate(dc, tc, timeScale);

  686.     }


  689.     /** Build an instance corresponding to a GPS date.
  690.      * <p>GPS dates are provided as a week number starting at
  691.      * {@link #GPS_EPOCH GPS epoch} and as a number of milliseconds
  692.      * since week start.</p>
  693.      * @param weekNumber week number since {@link #GPS_EPOCH GPS epoch}
  694.      * @param milliInWeek number of milliseconds since week start
  695.      * @return a new instant
  696.      * @deprecated as of 9.3, replaced by {@link GPSDate#GPSDate(int, double)}.{@link GPSDate#getDate()}
  697.      */
  698.     @Deprecated
  699.     public static AbsoluteDate createGPSDate(final int weekNumber, final double milliInWeek) {
  700.         return new GPSDate(weekNumber, milliInWeek).getDate();
  701.     }

  703.     /** Build an instance corresponding to a Julian Epoch (JE).
  704.      * <p>According to Lieske paper: <a
  705.      * href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&amp;defaultprint=YES&amp;filetype=.pdf.">
  706.      * Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
  707.      * vol. 73, no. 3, Mar. 1979, p. 282-284, Julian Epoch is related to Julian Ephemeris Date as:</p>
  708.      * <pre>
  709.      * JE = 2000.0 + (JED - 2451545.0) / 365.25
  710.      * </pre>
  711.      * <p>
  712.      * This method reverts the formula above and computes an {@code AbsoluteDate} from the Julian Epoch.
  713.      * </p>
  714.      * @param julianEpoch Julian epoch, like 2000.0 for defining the classical reference J2000.0
  715.      * @return a new instant
  716.      * @see #J2000_EPOCH
  717.      * @see #createBesselianEpoch(double)
  718.      */
  719.     public static AbsoluteDate createJulianEpoch(final double julianEpoch) {
  720.         return new AbsoluteDate(J2000_EPOCH,
  721.                                 Constants.JULIAN_YEAR * (julianEpoch - 2000.0));
  722.     }

  724.     /** Build an instance corresponding to a Besselian Epoch (BE).
  725.      * <p>According to Lieske paper: <a
  726.      * href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979A%26A....73..282L&amp;defaultprint=YES&amp;filetype=.pdf.">
  727.      * Precession Matrix Based on IAU (1976) System of Astronomical Constants</a>, Astronomy and Astrophysics,
  728.      * vol. 73, no. 3, Mar. 1979, p. 282-284, Besselian Epoch is related to Julian Ephemeris Date as:</p>
  729.      * <pre>
  730.      * BE = 1900.0 + (JED - 2415020.31352) / 365.242198781
  731.      * </pre>
  732.      * <p>
  733.      * This method reverts the formula above and computes an {@code AbsoluteDate} from the Besselian Epoch.
  734.      * </p>
  735.      * @param besselianEpoch Besselian epoch, like 1950 for defining the classical reference B1950.0
  736.      * @return a new instant
  737.      * @see #createJulianEpoch(double)
  738.      */
  739.     public static AbsoluteDate createBesselianEpoch(final double besselianEpoch) {
  740.         return new AbsoluteDate(J2000_EPOCH,
  741.                                 MathArrays.linearCombination(Constants.BESSELIAN_YEAR, besselianEpoch - 1900,
  742.                                                              Constants.JULIAN_DAY, -36525,
  743.                                                              Constants.JULIAN_DAY, 0.31352));
  744.     }

  746.     /** Get a time-shifted date.
  747.      * <p>
  748.      * Calling this method is equivalent to call <code>new AbsoluteDate(this, dt)</code>.
  749.      * </p>
  750.      * @param dt time shift in seconds
  751.      * @return a new date, shifted with respect to instance (which is immutable)
  752.      * @see org.orekit.utils.PVCoordinates#shiftedBy(double)
  753.      * @see org.orekit.attitudes.Attitude#shiftedBy(double)
  754.      * @see org.orekit.orbits.Orbit#shiftedBy(double)
  755.      * @see org.orekit.propagation.SpacecraftState#shiftedBy(double)
  756.      */
  757.     public AbsoluteDate shiftedBy(final double dt) {
  758.         return new AbsoluteDate(this, dt);
  759.     }

  761.     /** Compute the physically elapsed duration between two instants.
  762.      * <p>The returned duration is the number of seconds physically
  763.      * elapsed between the two instants, measured in a regular time
  764.      * scale with respect to surface of the Earth (i.e either the {@link
  765.      * TAIScale TAI scale}, the {@link TTScale TT scale} or the {@link
  766.      * GPSScale GPS scale}). It is the only method that gives a
  767.      * duration with a physical meaning.</p>
  768.      * <p>This method gives the same result (with less computation)
  769.      * as calling {@link #offsetFrom(AbsoluteDate, TimeScale)}
  770.      * with a second argument set to one of the regular scales cited
  771.      * above.</p>
  772.      * <p>This method is the reverse of the {@link #AbsoluteDate(AbsoluteDate,
  773.      * double)} constructor.</p>
  774.      * @param instant instant to subtract from the instance
  775.      * @return offset in seconds between the two instants (positive
  776.      * if the instance is posterior to the argument)
  777.      * @see #offsetFrom(AbsoluteDate, TimeScale)
  778.      * @see #AbsoluteDate(AbsoluteDate, double)
  779.      */
  780.     public double durationFrom(final AbsoluteDate instant) {
  781.         return (epoch - instant.epoch) + (offset - instant.offset);
  782.     }

  784.     /** Compute the apparent clock offset between two instant <em>in the
  785.      * perspective of a specific {@link TimeScale time scale}</em>.
  786.      * <p>The offset is the number of seconds counted in the given
  787.      * time scale between the locations of the two instants, with
  788.      * all time scale irregularities removed (i.e. considering all
  789.      * days are exactly 86400 seconds long). This method will give
  790.      * a result that may not have a physical meaning if the time scale
  791.      * is irregular. For example since a leap second was introduced at
  792.      * the end of 2005, the apparent offset between 2005-12-31T23:59:59
  793.      * and 2006-01-01T00:00:00 is 1 second, but the physical duration
  794.      * of the corresponding time interval as returned by the {@link
  795.      * #durationFrom(AbsoluteDate)} method is 2 seconds.</p>
  796.      * <p>This method is the reverse of the {@link #AbsoluteDate(AbsoluteDate,
  797.      * double, TimeScale)} constructor.</p>
  798.      * @param instant instant to subtract from the instance
  799.      * @param timeScale time scale with respect to which the offset should
  800.      * be computed
  801.      * @return apparent clock offset in seconds between the two instants
  802.      * (positive if the instance is posterior to the argument)
  803.      * @see #durationFrom(AbsoluteDate)
  804.      * @see #AbsoluteDate(AbsoluteDate, double, TimeScale)
  805.      */
  806.     public double offsetFrom(final AbsoluteDate instant, final TimeScale timeScale) {
  807.         final long   elapsedDurationA = epoch - instant.epoch;
  808.         final double elapsedDurationB = (offset         + timeScale.offsetFromTAI(this)) -
  809.                                         (instant.offset + timeScale.offsetFromTAI(instant));
  810.         return  elapsedDurationA + elapsedDurationB;
  811.     }

  813.     /** Compute the offset between two time scales at the current instant.
  814.      * <p>The offset is defined as <i>l₁-l₂</i>
  815.      * where <i>l₁</i> is the location of the instant in
  816.      * the <code>scale1</code> time scale and <i>l₂</i> is the
  817.      * location of the instant in the <code>scale2</code> time scale.</p>
  818.      * @param scale1 first time scale
  819.      * @param scale2 second time scale
  820.      * @return offset in seconds between the two time scales at the
  821.      * current instant
  822.      */
  823.     public double timeScalesOffset(final TimeScale scale1, final TimeScale scale2) {
  824.         return scale1.offsetFromTAI(this) - scale2.offsetFromTAI(this);
  825.     }

  827.     /** Convert the instance to a Java {@link java.util.Date Date}.
  828.      * <p>Conversion to the Date class induces a loss of precision because
  829.      * the Date class does not provide sub-millisecond information. Java Dates
  830.      * are considered to be locations in some times scales.</p>
  831.      * @param timeScale time scale to use
  832.      * @return a {@link java.util.Date Date} instance representing the location
  833.      * of the instant in the time scale
  834.      */
  835.     public Date toDate(final TimeScale timeScale) {
  836.         final double time = epoch + (offset + timeScale.offsetFromTAI(this));
  837.         return new Date(FastMath.round((time + 10957.5 * 86400.0) * 1000));
  838.     }

  840.     /** Split the instance into date/time components.
  841.      * @param timeScale time scale to use
  842.      * @return date/time components
  843.      */
  844.     public DateTimeComponents getComponents(final TimeScale timeScale) {

  846.         if (Double.isInfinite(offset)) {
  847.             // special handling for past and future infinity
  848.             if (offset < 0) {
  849.                 return new DateTimeComponents(DateComponents.MIN_EPOCH, TimeComponents.H00);
  850.             } else {
  851.                 return new DateTimeComponents(DateComponents.MAX_EPOCH,
  852.                                               new TimeComponents(23, 59, 59.999));
  853.             }
  854.         }

  856.         // compute offset from 2000-01-01T00:00:00 in specified time scale exactly,
  857.         // using Møller-Knuth TwoSum algorithm without branching
  858.         // the following statements must NOT be simplified, they rely on floating point
  859.         // arithmetic properties (rounding and representable numbers)
  860.         // at the end, the EXACT result of addition offset + timeScale.offsetFromTAI(this)
  861.         // is sum + residual, where sum is the closest representable number to the exact
  862.         // result and residual is the missing part that does not fit in the first number
  863.         final double taiOffset = timeScale.offsetFromTAI(this);
  864.         final double sum       = offset + taiOffset;
  865.         final double oPrime    = sum - taiOffset;
  866.         final double dPrime    = sum - oPrime;
  867.         final double deltaO    = offset - oPrime;
  868.         final double deltaD    = taiOffset - dPrime;
  869.         final double residual  = deltaO + deltaD;

  871.         // split date and time
  872.         final long   carry = (long) FastMath.floor(sum);
  873.         double offset2000B = (sum - carry) + residual;
  874.         long   offset2000A = epoch + carry + 43200l;
  875.         if (offset2000B < 0) {
  876.             offset2000A -= 1;
  877.             offset2000B += 1;
  878.         }
  879.         long time = offset2000A % 86400l;
  880.         if (time < 0l) {
  881.             time += 86400l;
  882.         }
  883.         final int date = (int) ((offset2000A - time) / 86400l);

  885.         // extract calendar elements
  886.         final DateComponents dateComponents = new DateComponents(DateComponents.J2000_EPOCH, date);
  887.         TimeComponents timeComponents = new TimeComponents((int) time, offset2000B);

  889.         if (timeScale.insideLeap(this)) {
  890.             // fix the seconds number to take the leap into account
  891.             timeComponents = new TimeComponents(timeComponents.getHour(), timeComponents.getMinute(),
  892.                                                 timeComponents.getSecond() + timeScale.getLeap(this));
  893.         }

  895.         // build the components
  896.         return new DateTimeComponents(dateComponents, timeComponents);

  898.     }

  900.     /** Split the instance into date/time components for a local time.
  901.      * @param minutesFromUTC offset in <em>minutes</em> from UTC (positive Eastwards UTC,
  902.      * negative Westward UTC)
  903.      * @return date/time components
  904.           * @since 7.2
  905.      */
  906.     public DateTimeComponents getComponents(final int minutesFromUTC) {

  908.         final DateTimeComponents utcComponents = getComponents(TimeScalesFactory.getUTC());

  910.         // shift the date according to UTC offset, but WITHOUT touching the seconds,
  911.         // as they may exceed 60.0 during a leap seconds introduction,
  912.         // and we want to preserve these special cases
  913.         final double seconds = utcComponents.getTime().getSecond();

  915.         int minute = utcComponents.getTime().getMinute() + minutesFromUTC;
  916.         final int hourShift;
  917.         if (minute < 0) {
  918.             hourShift = (minute - 59) / 60;
  919.         } else if (minute > 59) {
  920.             hourShift = minute / 60;
  921.         } else {
  922.             hourShift = 0;
  923.         }
  924.         minute -= 60 * hourShift;

  926.         int hour = utcComponents.getTime().getHour() + hourShift;
  927.         final int dayShift;
  928.         if (hour < 0) {
  929.             dayShift = (hour - 23) / 24;
  930.         } else if (hour > 23) {
  931.             dayShift = hour / 24;
  932.         } else {
  933.             dayShift = 0;
  934.         }
  935.         hour -= 24 * dayShift;

  937.         return new DateTimeComponents(new DateComponents(utcComponents.getDate(), dayShift),
  938.                                       new TimeComponents(hour, minute, seconds, minutesFromUTC));

  940.     }

  942.     /** Split the instance into date/time components for a time zone.
  943.      * @param timeZone time zone
  944.      * @return date/time components
  945.           * @since 7.2
  946.      */
  947.     public DateTimeComponents getComponents(final TimeZone timeZone) {
  948.         final long milliseconds = FastMath.round(1000 * offsetFrom(JAVA_EPOCH, TimeScalesFactory.getUTC()));
  949.         return getComponents(timeZone.getOffset(milliseconds) / 60000);
  950.     }

  952.     /** Compare the instance with another date.
  953.      * @param date other date to compare the instance to
  954.      * @return a negative integer, zero, or a positive integer as this date
  955.      * is before, simultaneous, or after the specified date.
  956.      */
  957.     public int compareTo(final AbsoluteDate date) {
  958.         return Double.compare(durationFrom(date),  0);
  959.     }

  961.     /** {@inheritDoc} */
  962.     public AbsoluteDate getDate() {
  963.         return this;
  964.     }

  966.     /** Check if the instance represent the same time as another instance.
  967.      * @param date other date
  968.      * @return true if the instance and the other date refer to the same instant
  969.      */
  970.     public boolean equals(final Object date) {

  972.         if (date == this) {
  973.             // first fast check
  974.             return true;
  975.         }

  977.         if ((date != null) && (date instanceof AbsoluteDate)) {
  978.             return durationFrom((AbsoluteDate) date) == 0;
  979.         }

  981.         return false;

  983.     }

  985.     /** Get a hashcode for this date.
  986.      * @return hashcode
  987.      */
  988.     public int hashCode() {
  989.         final long l = Double.doubleToLongBits(durationFrom(J2000_EPOCH));
  990.         return (int) (l ^ (l >>> 32));
  991.     }

  993.     /** Get a String representation of the instant location in UTC time scale.
  994.      * @return a string representation of the instance,
  995.      * in ISO-8601 format with milliseconds accuracy
  996.      */
  997.     public String toString() {
  998.         return toString(TimeScalesFactory.getUTC());
  999.     }

  1001.     /** Get a String representation of the instant location.
  1002.      * @param timeScale time scale to use
  1003.      * @return a string representation of the instance,
  1004.      * in ISO-8601 format with milliseconds accuracy
  1005.      */
  1006.     public String toString(final TimeScale timeScale) {
  1007.         return getComponents(timeScale).toString(timeScale.minuteDuration(this));
  1008.     }

  1010.     /** Get a String representation of the instant location for a local time.
  1011.      * @param minutesFromUTC offset in <em>minutes</em> from UTC (positive Eastwards UTC,
  1012.      * negative Westward UTC).
  1013.      * @return string representation of the instance,
  1014.      * in ISO-8601 format with milliseconds accuracy
  1015.           * @since 7.2
  1016.      */
  1017.     public String toString(final int minutesFromUTC) {
  1018.         final int minuteDuration = TimeScalesFactory.getUTC().minuteDuration(this);
  1019.         return getComponents(minutesFromUTC).toString(minuteDuration);
  1020.     }

  1022.     /** Get a String representation of the instant location for a time zone.
  1023.      * @param timeZone time zone
  1024.      * @return string representation of the instance,
  1025.      * in ISO-8601 format with milliseconds accuracy
  1026.           * @since 7.2
  1027.      */
  1028.     public String toString(final TimeZone timeZone) {
  1029.         final int minuteDuration = TimeScalesFactory.getUTC().minuteDuration(this);
  1030.         return getComponents(timeZone).toString(minuteDuration);
  1031.     }

  1033. }
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