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CalendricalCalculations.cs
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CalendricalCalculations.cs
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// CalendricalCalculations.cs
//
// (C) Ulrich Kunitz 2002
//
//
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
namespace System.Globalization {
//using System.Collections;
/*
/// <summary>A class that provides mathematical functions.</summary>
/// <remarks>
/// <para>
/// We are breaking the .Net
/// naming conventions to be compatible to the "Calendrical Calculations"
/// bool.
/// </para>
/// </remarks>
internal class CCMath {
/// <summary>
/// A static method which rounds a double value.
/// </summary>
/// <param name="x">The double value to round.</param>
/// <returns>The rounded double.</returns>
public static double round(double x) {
return System.Math.Floor(x+0.5);
}
/// <summary>
/// A static method that computes the remainder of the division
/// of two doubles.
/// </summary>
/// <param name="x">The double value which is divided.</param>
/// <param name="y">The divisor.</param>
/// <returns>The remainder as double value.</returns>
public static double mod(double x, double y) {
return x - y * System.Math.Floor(x/y);
}
/// <summary>
/// The static method divides two integers.
/// </summary>
/// <param name="x">The integer x value.</param>
/// <param name="y">The integer y value.</param>
/// <returns>The qotient of x and y defined by floor(x/y).
/// </returns>
/// <remarks>
/// Please notify that the function is not compatible to the standard
/// integer divide operation /.
/// </remarks>
public static int div(int x, int y) {
return (int)System.Math.Floor((double)x/(double)y);
}
/// <summary>
/// The static method computes the remainder of two integers.
/// </summary>
/// <param name="x">The integer value which will be divided.</param>
/// <param name="y">The divisor integer value.</param>
/// <returns> The remainder as integer value.</returns>
/// <remarks>
/// Please notify that the method is not compatible to the C#
/// remainder operation %.
/// </remarks>
public static int mod(int x, int y) {
return x - y * div(x, y);
}
/// <summary>
/// A static method that combines integer division and remainder
/// computation.
/// </summary>
/// <param name="remainder">Remainder integer output value.
/// </param>
/// <param name="x">Integer to be divided.</param>
/// <param name="y">Divisor integer value.</param>
/// <returns>The quotient as integer.</returns>
/// <seealso cref="M:div"/>
/// <seealso cref="M:mod"/>
public static int div_mod(out int remainder, int x, int y) {
int d = div(x, y);
remainder = x - y * d;
return d;
}
/// <summary>
/// A static method returning the sign of the argument.
/// </summary>
/// <param name="x">The double argument.</param>
/// <returns>An integer value: -1 for a negative argument;
/// 0 for a zero argument, and 1 for a positive argument.
/// </returns>
public static int signum(double x) {
if (x < 0.0)
return -1;
if (x == 0.0)
return 0;
return 1;
}
/// <summary>
/// A static method returning the sign of the integer
/// argument.
/// </summary>
/// <param name="x">The integer argument.</param>
/// <returns>An integer value: -1 for a negative argument;
/// 0 for a zero argument, and 1 for a positive argument.
/// </returns>
public static int signum(int x) {
if (x < 0)
return -1;
if (x == 0)
return 0;
return 1;
}
/// <summary>
/// An adjusted remainder function as defined in "Calendrical
/// Calculations".
/// </summary>
/// <param name="x">The double x argument.</param>
/// <param name="y">The double y argument, the divisor.</param>
/// <returns>A double value representing remainder; but instead 0.0
/// the divisor y is returned.
/// </returns>
public static double amod(double x, double y) {
double d = mod(x, y);
return (d == 0.0) ? y : d;
}
/// <summary>
/// The adjusted remainder functions for integers as defined in
/// "Calendrical Calculations".
/// </summary>
/// <param name="x">The integer argument to be divided.</param>
/// <param name="y">The integer divisor argument.</param>
/// <returns>The remainder as an integer; however instead 0
/// is the divisor y returned.
/// </returns>
public static int amod(int x, int y) {
int i = mod(x, y);
return (i == 0) ? y : i;
}
}
*/
/// <summary>The class implements methods to handle the fixed date value from
/// the "Calendrical Calculations" books.
/// </summary>
/// <remarks>
/// <para>
/// For implementing the Calendar classes I used the algorithms from the
/// book "Calendrical Calculations" by Nachum Dershowitz and Edward M.
/// Rheingold, second reprint 1998. Trying to prevent the introduction of new
/// bugs, I implemented their algorithms in the
/// <see cref="N:CalendricalCalculations"/>
/// namespace and wrapped it in the calendar classes.
/// </para>
/// <para>
/// The fixed day number is also known as R.D. - rata die.
/// Midnight at the onset of Monday,
/// January 1, year 1 (Gregorian) is R.D. 1.
/// </para>
/// <para>Here are all my references:</para>
/// <list type="table">
/// <item><description>
/// [1] Nachum Dershowitz and Edward M. Rheingold: "Calendrical Calculations";
/// Cambridge University Press; second reprint 1998.
/// </description></item>
/// <item><description>
/// [2] P. Kenneth Seidelmann (ed.): "Explanatory Supplement to the Astronomical
/// Almanac"; University Science Books, Sausalito; 1992
/// </description></item>
/// <item><description>
/// [3] F. Richard Stephenson: "Historical Eclipses and Earth Rotation";
/// Cambridge University Press; 1997
/// </description></item>
/// </list>
/// </remarks>
internal class CCFixed {
/// <summary>The method computes the
/// <see cref="T:System.DateTime"/>
/// from a fixed day number.
/// </summary>
/// <param name="date">A integer representing the fixed day number.
/// </param>
/// <returns>The <see cref="T:System.DateTime"/> representing
/// the date.
/// </returns>
public static System.DateTime ToDateTime(int date) {
long ticks = (date - 1) * System.TimeSpan.TicksPerDay;
return new System.DateTime(ticks);
}
/// <summary>The method computes the
/// <see cref="T:System.DateTime"/>
/// from a fixed day number and time arguments.
/// </summary>
/// <param name="date">An integer representing the fixed day number.
/// </param>
/// <param name="hour">An integer argument specifying the hour.
/// </param>
/// <param name="minute">An integer argument specifying the minute.
/// </param>
/// <param name="second">An integer argument giving the second.
/// </param>
/// <param name="milliseconds">An double argument specifying
/// the milliseconds. Notice that
/// <see cref="T:System.DateTime"/> has 100 nanosecond resolution.
/// </param>
/// <returns>The <see cref="T:System.DateTime"/> representing
/// the date.
/// </returns>
public static System.DateTime ToDateTime(int date,
int hour, int minute, int second, double milliseconds)
{
System.DateTime time = ToDateTime(date);
time = time.AddHours(hour);
time = time.AddMinutes(minute);
time = time.AddSeconds(second);
return time.AddMilliseconds(milliseconds);
}
/// <summary>
/// A static method computing the fixed day number from a
/// <see cref="T:System.DateTime"/> value.
/// </summary>
/// <param name="time">A
/// <see cref="T:System.DateTime"/> value representing the date.
/// </param>
/// <returns>The fixed day number as integer representing the date.
/// </returns>
public static int FromDateTime(System.DateTime time) {
return 1 + (int)(time.Ticks / System.TimeSpan.TicksPerDay);
}
/// <summary>
/// The static method computes the <see cref="T:DayOfWeek"/>.
/// </summary>
/// <param name="date">An integer representing the fixed day number.
/// </param>
/// <returns>The day of week.</returns>
public static DayOfWeek day_of_week(int date) {
return (DayOfWeek)(date % 7);//CCMath.mod(date, 7);
}
/// <summary>
/// The static method computes the date of a day of week on or before
/// a particular date.
/// </summary>
/// <param name="date">An integer representing the date as
/// fixed day number.
/// </param>
/// <param name="k">An integer representing the day of the week,
/// starting with 0 for sunday.
/// </param>
/// <returns>The fixed day number of the day of week specified by k
/// on or before the given date.
/// </returns>
public static int kday_on_or_before(int date, int k) {
return date - (int)day_of_week(date-k);
}
/// <summary>
/// The static method computes the date of a day of week on or after
/// a particular date.
/// </summary>
/// <param name="date">An integer representing the date as
/// fixed day number.
/// </param>
/// <param name="k">An integer representing the day of the week,
/// starting with 0 for sunday.
/// </param>
/// <returns>The fixed day number of the day of week specified by k
/// on or after the given date.
/// </returns>
public static int kday_on_or_after(int date, int k) {
return kday_on_or_before(date+6, k);
}
/// <summary>
/// The static method computes the date of a day of week that is
/// nearest to a particular date.
/// </summary>
/// <param name="date">An integer representing the date as
/// fixed day number.
/// </param>
/// <param name="k">An integer representing the day of the week,
/// starting with 0 for sunday.
/// </param>
/// <returns>The fixed day number of the day of week neares to the
/// given date.
/// </returns>
public static int kd_nearest(int date, int k) {
return kday_on_or_before(date+3, k);
}
/// <summary>
/// The static method computes the date of a day of week after
/// a particular date.
/// </summary>
/// <param name="date">An integer representing the date as
/// fixed day number.
/// </param>
/// <param name="k">An integer representing the day of the week,
/// starting with 0 for sunday.
/// </param>
/// <returns>The fixed day number of the day of week specified by k
/// after the given date.
/// </returns>
public static int kday_after(int date, int k) {
return kday_on_or_before(date+7, k);
}
/// <summary>
/// The static method computes the date of a day of week before
/// a particular date.
/// </summary>
/// <param name="date">An integer representing the date as
/// fixed day number.
/// </param>
/// <param name="k">An integer representing the day of the week,
/// starting with 0 for sunday.
/// </param>
/// <returns>The fixed day number of the day of week specified by k
/// before the given date.
/// </returns>
public static int kday_before(int date, int k) {
return kday_on_or_before(date-1, k);
}
} // class CCFixed
/// <summary>
/// A class encapsulating the functions of the Gregorian calendar as static
/// methods.
/// </summary>
/// <remarks>
/// <para>
/// This class is not compatible to
/// <see cref="T:System.Globalization.GregorianCalendar"/>.
/// </para>
/// <para>
/// The fixed day number is also known as R.D. - rata die.
/// Midnight at the onset of Monday,
/// January 1, year 1 (Gregorian) is R.D. 1.
/// </para>
/// <seealso cref="T:CCFixed"/>
/// </remarks>
internal class CCGregorianCalendar {
/// <summary>An integer defining the epoch of the Gregorian calendar
/// as fixed day number.</summary>
/// <remarks>The epoch is January 3, 1 C.E. (Julian).</remarks>
const int epoch = 1;
/// <summary>The enumeration defines the months of the Gregorian
/// calendar.
/// </summary>
public enum Month {
/// <summary>
/// January.
/// </summary>
january = 1,
/// <summary>
/// February.
/// </summary>
february,
/// <summary>
/// March.
/// </summary>
march,
/// <summary>
/// April.
/// </summary>
april,
/// <summary>
/// May.
/// </summary>
may,
/// <summary>
/// June.
/// </summary>
june,
/// <summary>
/// July.
/// </summary>
july,
/// <summary>
/// August.
/// </summary>
august,
/// <summary>
/// September.
/// </summary>
september,
/// <summary>
/// October.
/// </summary>
october,
/// <summary>
/// November.
/// </summary>
november,
/// <summary>
/// December.
/// </summary>
december
};
/// <summary>
/// The method tells whether the year is a leap year.
/// </summary>
/// <param name="year">An integer representing the Gregorian year.
/// </param>
/// <returns>A boolean which is true if <paramref name="year"/> is
/// a leap year.
/// </returns>
public static bool is_leap_year(int year) {
if (year % 4 != 0)
return false;
switch (year % 400) {
case 100:
return false;
case 200:
return false;
case 300:
return false;
}
return true;
}
/// <summary>
/// The method returns the fixed day number of the given Gregorian
/// date.
/// </summary>
/// <param name="day">An integer representing the day of the month,
/// counting from 1.
/// </param>
/// <param name="month">An integer representing the month in the
/// Gregorian year.
/// </param>
/// <param name="year">An integer representing the Gregorian year.
/// Non-positive values are allowed also.
/// </param>
/// <returns>An integer value representing the fixed day number.
/// </returns>
public static int fixed_from_dmy(int day, int month, int year) {
int k = epoch - 1;
k += 365 * (year-1);
//k += CCMath.div(year-1, 4);
//k -= CCMath.div(year-1, 100);
//k += CCMath.div(year-1, 400);
//k += CCMath.div(367*month-362, 12);
k += (year - 1) / 4;
k -= (year - 1) / 100;
k += (year - 1) / 400;
k += (367 * month - 362) / 12;
if (month > 2) {
k -= is_leap_year(year) ? 1 : 2;
}
k += day;
return k;
}
/// <summary>
/// The method computes the Gregorian year from a fixed day number.
/// </summary>
/// <param name="date">The fixed day number.
/// </param>
/// <returns>An integer value giving the Gregorian year of the date.
/// </returns>
public static int year_from_fixed(int date) {
int d = date - epoch;
int n_400 = d / 146097;
d %= 146097;
int n_100 = d / 36524;
d %= 36524;
int n_4 = d / 1461;
d %= 1461;
int n_1 = d / 365;
//int n_400 = CCMath.div_mod(out d, d, 146097);
//int n_100 = CCMath.div_mod(out d, d, 36524);
//int n_4 = CCMath.div_mod(out d, d, 1461);
//int n_1 = CCMath.div(d, 365);
int year = 400*n_400 + 100*n_100 + 4*n_4 + n_1;
return (n_100 == 4 || n_1 == 4) ? year : year + 1;
}
/// <summary>
/// The method computes the Gregorian year and month from a fixed day
/// number.
/// </summary>
/// <param name="month">The output value giving the Gregorian month.
/// </param>
/// <param name="year">The output value giving the Gregorian year.
/// </param>
/// <param name="date">An integer value specifying the fixed day
/// number.</param>
public static void my_from_fixed(out int month, out int year,
int date)
{
year = year_from_fixed(date);
int prior_days = date - fixed_from_dmy(1, (int)Month.january,
year);
int correction;
if (date < fixed_from_dmy(1, (int)Month.march, year)) {
correction = 0;
} else if (is_leap_year(year)) {
correction = 1;
} else {
correction = 2;
}
//month = CCMath.div(12 * (prior_days + correction) + 373, 367);
month = (12 * (prior_days + correction) + 373) / 367;
}
/// <summary>
/// The method computes the Gregorian year, month, and day from a
/// fixed day number.
/// </summary>
/// <param name="day">The output value returning the day of the
/// month.
/// </param>
/// <param name="month">The output value giving the Gregorian month.
/// </param>
/// <param name="year">The output value giving the Gregorian year.
/// </param>
/// <param name="date">An integer value specifying the fixed day
/// number.</param>
public static void dmy_from_fixed(out int day, out int month,
out int year,
int date)
{
my_from_fixed(out month, out year, date);
day = date - fixed_from_dmy(1, month, year) + 1;
}
/// <summary>A method computing the Gregorian month from a fixed
/// day number.
/// </summary>
/// <param name="date">An integer specifying the fixed day number.
/// </param>
/// <returns>An integer value representing the Gregorian month.
/// </returns>
public static int month_from_fixed(int date) {
int month, year;
my_from_fixed(out month, out year, date);
return month;
}
/// <summary>
/// A method computing the day of the month from a fixed day number.
/// </summary>
/// <param name="date">An integer specifying the fixed day number.
/// </param>
/// <returns>An integer value representing the day of the month.
/// </returns>
public static int day_from_fixed(int date) {
int day, month, year;
dmy_from_fixed(out day, out month, out year, date);
return day;
}
/// <summary>
/// The method computes the difference between two Gregorian dates.
/// </summary>
/// <param name="dayA">The integer parameter gives the day of month
/// of the first date.
/// </param>
/// <param name="monthA">The integer parameter gives the Gregorian
/// month of the first date.
/// </param>
/// <param name="yearA">The integer parameter gives the Gregorian
/// year of the first date.
/// </param>
/// <param name="dayB">The integer parameter gives the day of month
/// of the second date.
/// </param>
/// <param name="monthB">The integer parameter gives the Gregorian
/// month of the second date.
/// </param>
/// <param name="yearB">The integer parameter gives the Gregorian
/// year of the second date.
/// </param>
/// <returns>An integer giving the difference of days from the first
/// the second date.
/// </returns>
public static int date_difference(int dayA, int monthA, int yearA,
int dayB, int monthB, int yearB)
{
return fixed_from_dmy(dayB, monthB, yearB) -
fixed_from_dmy(dayA, monthA, yearA);
}
/// <summary>
/// The method computes the number of the day in the year from
/// a Gregorian date.
/// </summary>
/// <param name="day">An integer representing the day of the month,
/// counting from 1.
/// </param>
/// <param name="month">An integer representing the month in the
/// Gregorian year.
/// </param>
/// <param name="year">An integer representing the Gregorian year.
/// Non-positive values are allowed also.
/// </param>
/// <returns>An integer value giving the number of the day in the
/// Gregorian year, counting from 1.
/// </returns>
public static int day_number(int day, int month, int year) {
return date_difference(31, (int)Month.december, year-1,
day, month, year);
}
/// <summary>
/// The method computes the days remaining in the given Gregorian
/// year from a Gregorian date.
/// </summary>
/// <param name="day">An integer representing the day of the month,
/// counting from 1.
/// </param>
/// <param name="month">An integer representing the month in the
/// Gregorian year.
/// </param>
/// <param name="year">An integer representing the Gregorian year.
/// Non-positive values are allowed also.
/// </param>
/// <returns>An integer value giving the number of days remaining in
/// the Gregorian year.
/// </returns>
public static int days_remaining(int day, int month, int year) {
return date_difference(day, month, year,
31, (int)Month.december, year);
}
// Helper functions for the Gregorian calendars.
/// <summary>
/// Adds months to the given date.
/// </summary>
/// <param name="time">The
/// <see cref="T:System.DateTime"/> to which to add
/// months.
/// </param>
/// <param name="months">The number of months to add.</param>
/// <returns>A new <see cref="T:System.DateTime"/> value, that
/// results from adding <paramref name="months"/> to the specified
/// DateTime.</returns>
public static System.DateTime AddMonths(System.DateTime time,
int months)
{
int rd = CCFixed.FromDateTime(time);
int day, month, year;
dmy_from_fixed(out day, out month, out year, rd);
month += months;
int maxday = GetDaysInMonth (year, month);
if (day > maxday)
day = maxday;
rd = fixed_from_dmy(day, month, year);
System.DateTime t = CCFixed.ToDateTime(rd);
return t.Add(time.TimeOfDay);
}
/// <summary>
/// Adds years to the given date.
/// </summary>
/// <param name="time">The
/// <see cref="T:System.DateTime"/> to which to add
/// months.
/// </param>
/// <param name="years">The number of years to add.</param>
/// <returns>A new <see cref="T:System.DateTime"/> value, that
/// results from adding <paramref name="years"/> to the specified
/// DateTime.</returns>
public static System.DateTime AddYears(System.DateTime time,
int years)
{
int rd = CCFixed.FromDateTime(time);
int day, month, year;
dmy_from_fixed(out day, out month, out year, rd);
year += years;
int maxday = GetDaysInMonth (year, month);
if (day > maxday)
day = maxday;
rd = fixed_from_dmy(day, month, year);
System.DateTime t = CCFixed.ToDateTime(rd);
return t.Add(time.TimeOfDay);
}
/// <summary>
/// Gets the of the month from <paramref name="time"/>.
/// </summary>
/// <param name="time">The
/// <see cref="T:System.DateTime"/> that specifies a
/// date.
/// </param>
/// <returns>An integer giving the day of months, starting with 1.
/// </returns>
public static int GetDayOfMonth(System.DateTime time) {
return day_from_fixed(CCFixed.FromDateTime(time));
}
/// <summary>
/// The method gives the number of the day in the year.
/// </summary>
/// <param name="time">The
/// <see cref="T:System.DateTime"/> that specifies a
/// date.
/// </param>
/// <returns>An integer representing the day of the year,
/// starting with 1.</returns>
public static int GetDayOfYear(System.DateTime time) {
int rd = CCFixed.FromDateTime(time);
int year = year_from_fixed(rd);
int rd1_1 = fixed_from_dmy(1, 1, year);
return rd - rd1_1 + 1;
}
/// <summary>
/// A method that gives the number of days of the specified
/// month of the <paramref name="year"/>.
/// </summary>
/// <param name="year">An integer that gives the year in the current
/// era.</param>
/// <param name="month">An integer that gives the month, starting
/// with 1.</param>
/// <returns>An integer that gives the number of days of the
/// specified month.</returns>
public static int GetDaysInMonth(int year, int month) {
int rd1 = fixed_from_dmy(1, month, year);
int rd2 = fixed_from_dmy(1, month+1, year);
return rd2 - rd1;
}
/// <summary>
/// The method gives the number of days in the specified year.
/// </summary>
/// <param name="year">An integer that gives the year.
/// </param>
/// <returns>An integer that gives the number of days of the
/// specified year.</returns>
public static int GetDaysInYear(int year) {
int rd1 = fixed_from_dmy(1, 1, year);
int rd2 = fixed_from_dmy(1, 1, year+1);
return rd2 - rd1;
}
/// <summary>
/// The method gives the number of the month of the specified
/// date.
/// </summary>
/// <param name="time">The
/// <see cref="T:System.DateTime"/> that specifies a
/// date.
/// </param>
/// <returns>An integer representing the month,
/// starting with 1.</returns>
public static int GetMonth(System.DateTime time) {
return month_from_fixed(CCFixed.FromDateTime(time));
}
/// <summary>
/// The method gives the number of the year of the specified
/// date.
/// </summary>
/// <param name="time">The
/// <see cref="T:System.DateTime"/> that specifies a
/// date.
/// </param>
/// <returns>An integer representing the year.
/// </returns>
public static int GetYear(System.DateTime time) {
return year_from_fixed(CCFixed.FromDateTime(time));
}
/// <summary>
/// A virtual method that tells whether the given day
/// is a leap day.
/// </summary>
/// <param name="year">An integer that specifies the year.
/// </param>
/// <param name="month">An integer that specifies the month.
/// </param>
/// <param name="day">An integer that specifies the day.
/// </param>
/// <returns>A boolean that tells whether the given day is a leap
/// day.
/// </returns>
public static bool IsLeapDay(int year, int month, int day) {
return is_leap_year(year) && month == 2 && day == 29;
}
/// <summary>
/// A method that creates the
/// <see cref="T:System.DateTime"/> from the parameters.
/// </summary>
/// <param name="year">An integer that gives the year
/// </param>
/// <param name="month">An integer that specifies the month.
/// </param>
/// <param name="day">An integer that specifies the day.
/// </param>
/// <param name="hour">An integer that specifies the hour.
/// </param>
/// <param name="minute">An integer that specifies the minute.
/// </param>
/// <param name="second">An integer that gives the second.
/// </param>
/// <param name="milliseconds">An integer that gives the
/// milliseconds.
/// </param>
/// <returns>A
/// <see cref="T:system.DateTime"/> representig the date and time.
/// </returns>
public static System.DateTime ToDateTime(int year, int month, int day,
int hour, int minute, int second, int milliseconds)
{
return CCFixed.ToDateTime(fixed_from_dmy(day, month, year),
hour, minute, second, milliseconds);
}
} // class CCGregorianCalendar
/*
/// <summary>
/// A class encapsulating the functions of the Julian calendar as static
/// methods.
/// </summary>
/// <remarks>
/// <para>The algorithms don't support a year 0. Years before Common Era
/// (B.C.E. or B.C.) are negative and years of Common Era (C.E. or A.D.)
/// are positive.
/// </para>
/// <para>
/// This class is not compatible to
/// <see cref="T:System.Globalization.JulianCalendar"/>.
/// </para>
/// <seealso cref="T:CCFixed"/>
/// </remarks>
internal class CCJulianCalendar {
/// <summary>An integer defining the epoch of the Julian calendar
/// as fixed day number.</summary>
/// <remarks>The epoch is December 30, 0 (Gregorian).</remarks>
const int epoch = -1; // 30. 12. 0 Gregorian
/// <summary>The enumeration defines the months of the Julian
/// calendar.
/// </summary>
public enum Month {
/// <summary>
/// January.
/// </summary>
january = 1,
/// <summary>
/// February.
/// </summary>
february,
/// <summary>
/// March.
/// </summary>
march,
/// <summary>
/// April.
/// </summary>
april,
/// <summary>
/// May.
/// </summary>
may,
/// <summary>
/// June.
/// </summary>
june,
/// <summary>
/// July.
/// </summary>
july,
/// <summary>
/// August.
/// </summary>
august,
/// <summary>
/// September.
/// </summary>
september,
/// <summary>
/// October.
/// </summary>
october,
/// <summary>
/// November.
/// </summary>
november,
/// <summary>
/// December.
/// </summary>
december
};
/// <summary>
/// The method tells whether the year is a leap year.
/// </summary>
/// <param name="year">An integer representing the Julian year.
/// </param>
/// <returns>A boolean which is true if <paramref name="year"/> is
/// a leap year.
/// </returns>
public static bool is_leap_year(int year) {
return CCMath.mod(year, 4) == (year > 0 ? 0 : 3);
}
/// <summary>
/// The method returns the fixed day number of the given Julian
/// date.
/// </summary>
/// <param name="day">An integer representing the day of the month,
/// counting from 1.
/// </param>
/// <param name="month">An integer representing the month in the
/// Julian year.
/// </param>
/// <param name="year">An integer representing the Julian year.
/// Positive and Negative values are allowed.
/// </param>
/// <returns>An integer value representing the fixed day number.
/// </returns>
public static int fixed_from_dmy(int day, int month, int year) {
int y = year < 0 ? year+1 : year;
int k = epoch - 1;
k += 365 * (y-1);
k += CCMath.div(y-1, 4);
k += CCMath.div(367*month-362, 12);
if (month > 2) {
k += is_leap_year(year) ? -1 : -2;
}
k += day;
return k;
}
/// <summary>
/// The method computes the Julian year from a fixed day number.
/// </summary>
/// <param name="date">The fixed day number.
/// </param>
/// <returns>An integer value giving the Julian year of the date.
/// </returns>
public static int year_from_fixed(int date) {
int approx = CCMath.div(4*(date-epoch)+1464, 1461);
return approx <= 0 ? approx - 1 : approx;
}
/// <summary>
/// The method computes the Julian year and month from a fixed day
/// number.
/// </summary>
/// <param name="month">The output value giving the Julian month.
/// </param>
/// <param name="year">The output value giving the Julian year.
/// </param>
/// <param name="date">An integer value specifying the fixed day
/// number.</param>
public static void my_from_fixed(out int month, out int year, int date)
{
year = year_from_fixed(date);
int prior_days = date - fixed_from_dmy(1, (int)Month.january,
year);