GenericParameter.cs: override Module properly

[mcs.git] / class / corlib / System.Globalization / CalendricalCalculations.cs

// 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)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 (CCMath.mod(year, 4) != 0)
                        return false;
                switch (CCMath.mod(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);
                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       = 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);

        }

        /// <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;
                year += CCMath.div_mod(out month, month, 12);
                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);
                
                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);
        }
        

        /// <summary>
        /// The method computes the Julian 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 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 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 Julian month from a fixed
        /// day number.
        /// </summary>
        /// <param name="date">An integer specifying the fixed day number.
        /// </param>
        /// <returns>An integer value representing the Julian 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;
                int month;
                int year;

                dmy_from_fixed(out day, out month, out year, date);
                return day;
        }

        /// <summary>
        /// The method computes the difference between two Julian 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 Julian
        /// month of the first date.
        /// </param>
        /// <param name="yearA">The integer parameter gives the Julian
        /// 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 Julian
        /// month of the second date.
        /// </param>
        /// <param name="yearB">The integer parameter gives the Julian
        /// 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 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.
        /// Negative values are allowed also.
        /// </param>
        /// <returns>An integer value giving the number of the day in the
        /// Julian 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 Julian
        /// year from a 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.
        /// Negative values are allowed also.
        /// </param>
        /// <returns>An integer value giving the number of days remaining in
        /// the Julian year.
        /// </returns>
        public static int days_remaining(int day, int month, int year) {
                return date_difference(day, month, year,
                        31, (int)Month.december, year);
        }
} // class CCJulianCalendar

/// <summary>
/// A class encapsulating the functions of the Hebrew calendar as static
/// methods.
/// </summary>
/// <remarks>
/// <para>
/// This class is not compatible to
/// <see cref="T:System.Globalization.HebrewCalendar"/>.
/// </para>
/// <seealso cref="T:CCFixed"/>
/// </remarks>
internal class CCHebrewCalendar {
        /// <summary>An integer defining the epoch of the Hebrew calendar
        /// as fixed day number.</summary>
        /// <remarks>The epoch is October 10, 3761 B.C.E. (Julian).</remarks>
        const int epoch = -1373427;

        /// <summary>The enumeration defines the months of the Gregorian
        /// calendar.
        /// </summary>
        /// <remarks>
        /// The enumaration differs from .NET which defines Tishri as month 1.
        /// </remarks>
        public enum Month {
                /// <summary>
                /// Nisan.
                /// </summary>
                nisan    = 1,
                /// <summary>
                /// Iyyar.
                /// </summary>
                iyyar,
                /// <summary>
                /// Sivan.
                /// </summary>
                sivan,
                /// <summary>
                /// Tammuz.
                /// </summary>
                tammuz,
                /// <summary>
                /// Av.
                /// </summary>
                av,
                /// <summary>
                /// Elul.
                /// </summary>
                elul,
                /// <summary>
                /// Tishri.
                /// </summary>
                tishri,
                /// <summary>
                /// Heshvan.
                /// </summary>
                heshvan,
                /// <summary>
                /// Kislev.
                /// </summary>
                kislev,
                /// <summary>
                /// Teveth.
                /// </summary>
                teveth,
                /// <summary>
                /// Shevat.
                /// </summary>
                shevat,
                /// <summary>
                /// Adar.
                /// </summary>
                adar,
                /// <summary>
                /// Adar I. Only in years with Adar II.
                /// </summary>
                adar_I = 12,
                /// <summary>
                /// Adar II. Only in years wirh Adar I.
                /// </summary>
                adar_II = 13,
        };

        /// <summary>
        /// The method tells whether the year is a leap year.
        /// </summary>
        /// <param name="year">An integer representing the Hebrew 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(7*year+1, 19) < 7; 
        }

        /// <summary>
        /// The Method gives the number of the last month in a year, which
        /// is equal with the number of month in a Hebrew year.
        /// </summary>
        /// <param name="year">An integer representing the Hebrew year.
        /// </param>
        /// <returns>An integer giving the number of the last month of the 
        /// Hebrew year, which is the same as the numbers of month in the
        /// year.
        /// </returns>
        public static int last_month_of_year(int year) {
                return is_leap_year(year) ? 13 : 12;
        }

        
        /// <summary>The method is a helper function.</summary>
        /// <param name="year">An integer specifying the Hebrew year.
        /// </param>
        /// <returns>An integer representing the number of elapsed days
        /// until the Hebrew year.</returns>
        public static int elapsed_days(int year) {
                int months_elapsed = CCMath.div(235*year-234, 19);
                int r;
                int d = CCMath.div_mod(out r, months_elapsed, 1080);
                int parts_elapsed = 204 + 793 * r;
                int hours_elapsed = 11 + 12 * months_elapsed +
                                    793 * d + CCMath.div(parts_elapsed, 1080);

                int day = 29*months_elapsed + CCMath.div(hours_elapsed, 24);

                if (CCMath.mod(3*(day+1), 7) < 3) {
                        day += 1;
                }

                return day;
        }

        /// <summary>A method computing the delay of new year for the given
        /// Hebrew year.
        /// </summary>
        /// <param name="year">An integer that gives the Hebrew year.
        /// </param>
        /// <returns>The new year delay in days of the given Hebrew year.
        /// </returns>
        public static int new_year_delay(int year) {
                int ny1 = elapsed_days(year);
                int ny2 = elapsed_days(year+1);

                if (ny2 - ny1 == 356) {
                        return 2;
                }
                int ny0 = elapsed_days(year-1);
                if (ny1 - ny0 == 382) {
                        return 1;
                }
                return 0;
        }

        /// <summary>
        /// The method computes the last day of month (nummer of days in a
        /// month) of the given Hebrew year.
        /// </summary>
        /// <param name="month">The Hebrew month, allowed value between
        /// One and Thirteen.
        /// </param>
        /// <param name="year">An integer that gives the Hebrew year.
        /// </param>
        /// <returns>The number of the last day of the month of the given
        /// Hebrew year, which gives automatically the number of days in the
        /// month.
        /// </returns>
        /// <exception cref="T:System.ArgumentOutOfRange.Exception">
        /// The exception is thrown if month not between One and Thirteen.
        /// </exception>
        public static int last_day_of_month(int month, int year) {
                if (month < 1 || month > 13)
                        throw new System.ArgumentOutOfRangeException("month",
                                "Month should be between One and Thirteen.");
                switch (month) {
                        case 2: return 29;
                        case 4: return 29;
                        case 6: return 29;
                        case 8:
                                if (!long_heshvan(year))
                                        return 29;
                                break;
                        case 9:
                                if (short_kislev(year))
                                        return 29;
                                break;
                        case 10: return 29;
                        case 12:
                                if (!is_leap_year(year))
                                        return 29;
                                break;
                        case 13: return 29;
                }
                return 30;
        }
        
        /// <summary>
        /// The functions checks whether the month Heshvan is a long one
        /// in the given Hebrew year.
        /// </summary>
        /// <param name="year">An integer that gives the Hebrew year.
        /// </param>
        /// <returns>A boolean value: true if there is a long Heshvan
        /// in the given Hebrew year; false otherwise.
        /// </returns>
        public static bool long_heshvan(int year) {
                return CCMath.mod(days_in_year(year), 10) == 5;
        }

        /// <summary>
        /// The functions checks whether the month Kislev is a short one
        /// in the given Hebrew year.
        /// </summary>
        /// <param name="year">An integer that gives the Hebrew year.
        /// </param>
        /// <returns>A boolean value: true if there is a short Kislev
        /// in the given Hebrew year; false otherwise.
        /// </returns>
        public static bool short_kislev(int year) {
                return CCMath.mod(days_in_year(year), 10) == 3;
        }

        /// <summary>
        /// The functions gives the number of days in the specified Hebrew
        /// year.
        /// </summary>
        /// <param name="year">An integer that gives the Hebrew year.
        /// </param>
        /// <returns>The days of the Hebrew year as integer.
        /// </returns>
        public static int days_in_year(int year) {
                return  fixed_from_dmy(1, 7, year+1) -
                        fixed_from_dmy(1, 7, year);
        }

        /// <summary>
        /// The method returns the fixed day number of the given Hebrew
        /// 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
        /// Hebrew year.
        /// </param>
        /// <param name="year">An integer representing the Hebrew 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 m;
                int k = epoch-1;
                k += elapsed_days(year);
                k += new_year_delay(year);

                if (month < 7) {
                        int l = last_month_of_year(year);
                        for (m = 7; m <= l; m++) {
                                k += last_day_of_month(m, year);
                        }
                        for (m = 1; m < month; m++) {
                                k += last_day_of_month(m, year);
                        }
                }
                else {
                        for (m = 7; m < month; m++) {
                                k += last_day_of_month(m, year);
                        }
                }
                
                k += day;

                return k;
        }

        /// <summary>
        /// The method computes the Hebrew year from a fixed day number.
        /// </summary>
        /// <param name="date">The fixed day number.
        /// </param>
        /// <returns>An integer value giving the Hebrew year of the date.
        /// </returns>
        public static int year_from_fixed(int date) {
                int approx = (int)System.Math.Floor(
                        ((double)(date - epoch))/(35975351.0/98496.0));
                int y;
                for (y = approx; date >= fixed_from_dmy(1, 7, y); y++) {} 
                return y-1;
        }

        /// <summary>
        /// The method computes the Hebrew year and month from a fixed day
        /// number.
        /// </summary>
        /// <param name="month">The output value giving the Hebrew month.
        /// </param>
        /// <param name="year">The output value giving the Hebrew 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 start = date < fixed_from_dmy(1, 1, year) ? 7 : 1;

                for (month = start;
                     date > fixed_from_dmy(last_day_of_month(month, year),
                                                month, year);
                     month++)
                {}
        }

        /// <summary>
        /// The method computes the Hebrew 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 Hebrew month.
        /// </param>
        /// <param name="year">The output value giving the Hebrew 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 Hebrew month from a fixed
        /// day number.
        /// </summary>
        /// <param name="date">An integer specifying the fixed day number.
        /// </param>
        /// <returns>An integer value representing the Hebrew 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 Hebrew 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 Hebrew
        /// month of the first date.
        /// </param>
        /// <param name="yearA">The integer parameter gives the Hebrew
        /// 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 Hebrew
        /// month of the second date.
        /// </param>
        /// <param name="yearB">The integer parameter gives the Hebrew
        /// 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 Hebrew 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
        /// Hebrew year.
        /// </param>
        /// <param name="year">An integer representing the Hebrew year.
        /// </param>
        /// <returns>An integer value giving the number of the day in the
        /// Hebrew year, counting from 1.
        /// </returns>
        public static int day_number(int day, int month, int year) {
                return date_difference(1, 7, year,
                        day, month, year) + 1;
        }

        /// <summary>
        /// The method computes the days remaining in the given Hebrew
        /// year from a Hebrew 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
        /// Hebrew year.
        /// </param>
        /// <param name="year">An integer representing the Hebrew year.
        /// </param>
        /// <returns>An integer value giving the number of days remaining in
        /// the Hebrew year.
        /// </returns>
        public static int days_remaining(int day, int month, int year) {
                return date_difference(day, month, year,
                        1, 7, year+1)-1;
        }
} // class HebrewCalendar


/// <summary>
/// A class encapsulating the functions of the Islamic calendar as static
/// methods.
/// </summary>
/// <remarks>
/// <para>There is no difference here in using Hijri or Islamic calendar.
/// </para>
/// <para>The epoch of the Islamic calendar isn't fixed, because we cannot
/// surely say today, when the crescent of the new moon has been observed 
/// around the July 16, 622 C.E. Julian. Even today the start and end of 
/// the month Ramadan is defined by religous authorities. So the calendar
/// can be offset by two days.
/// </para> 
/// <para>
/// We don't support the offset here, however we changed the epoch from
/// "Calendrical Calculations" to value, that .Net seems to be using.
/// </para>
/// <para>
/// This class is not compatible to
/// <see cref="T:System.Globalization.HijriCalendar"/>.
/// </para>
/// <seealso cref="T:CCFixed"/>
/// </remarks>
internal class CCHijriCalendar {
        /// <summary>An integer defining the epoch of the Gregorian calendar
        /// as fixed day number.</summary>
        /// <remarks>
        /// <para>
        /// The epoch is given as 16 July 622 C.E. Julian (R.D. 227015)
        /// in Calendrical Calculations, the approximate date of
        /// the emigration of
        /// Muhammed to Medina. However there is no way to determine today
        /// the observation of the crescent of the new moon in July 622 C.E.
        /// (Julian). So there is some variability in the epoch.
        /// Religous authorities determine the epoch by observing the
        /// crescent of the new moon for the month Ramadan, so there might
        /// be an offsets by two days of the epoch.
        /// </para>
        /// <para>Windows
        /// supports an AddHijriDate parameter in the registry to adapt
        /// for it. It seems that the .NET implementation of
        /// HijriCalendar uses an epoch of 227014, so we use it here. The
        /// ArgumentOutOfRangeException gives July, 18 622 as epoch,
        /// which is 227014 supporting our theory.
        /// </para>
        /// </remarks>
        const int epoch = 227014;

        /// <summary>The enumeration defines the months of the Islamic
        /// calendar.
        /// </summary>
        public enum Month {
                /// <summary>
                /// Muharram.
                /// </summary>
                muharram = 1,
                /// <summary>
                /// Safar.
                /// </summary>
                safar,
                /// <summary>
                /// Rabi I.
                /// </summary>
                rabi_I,
                /// <summary>
                /// Rabi II.
                /// </summary>
                rabi_II,
                /// <summary>
                /// Jumada I.
                /// </summary>
                jumada_I,
                /// <summary>
                /// Jumada II.
                /// </summary>
                jumada_II,
                /// <summary>
                /// Rajab.
                /// </summary>
                rajab,
                /// <summary>
                /// Shaban.
                /// </summary>
                shaban,
                /// <summary>
                /// Ramadan.
                /// </summary>
                ramadan,
                /// <summary>
                /// Shawwal.
                /// </summary>
                shawwal,
                /// <summary>
                /// Dhu Al-Quada.
                /// </summary>
                dhu_al_quada,
                /// <summary>
                /// Dhu Al-Hijja.
                /// </summary>
                dhu_al_hijja,
        };

        /// <summary>
        /// The method tells whether the year is a leap year.
        /// </summary>
        /// <param name="year">An integer representing the Islamic 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(14+11*year, 30) < 11;
        }

        /// <summary>
        /// The method returns the fixed day number of the given Islamic
        /// 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
        /// Islamic year.
        /// </param>
        /// <param name="year">An integer representing the Islamic 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 += 354 * (year-1);
                k += CCMath.div(3+11*year, 30);
                k += (int)System.Math.Ceiling(29.5 * (double)(month-1));
                k += day;

                return k;
        }

        /// <summary>
        /// The method computes the Islamic year from a fixed day number.
        /// </summary>
        /// <param name="date">The fixed day number.
        /// </param>
        /// <returns>An integer value giving the Islamic year of the date.
        /// </returns>
        public static int year_from_fixed(int date) {
                return CCMath.div(30*(date-epoch)+10646, 10631);
        }

        /// <summary>
        /// The method computes the Islamic year and month from a fixed day
        /// number.
        /// </summary>
        /// <param name="month">The output value giving the Islamic month.
        /// </param>
        /// <param name="year">The output value giving the Islamic 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 m = 1+(int)System.Math.Ceiling(
                        ((double)(date-29-fixed_from_dmy(1,1,year)))/29.5);

                month = m < 12 ? m : 12;
        }
        
        /// <summary>
        /// The method computes the Islamic 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 Islamic month.
        /// </param>
        /// <param name="year">The output value giving the Islamic 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 Islamic month from a fixed
        /// day number.
        /// </summary>
        /// <param name="date">An integer specifying the fixed day number.
        /// </param>
        /// <returns>An integer value representing the Islamic 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;
                int month;
                int year;

                dmy_from_fixed(out day, out month, out year, date);
                return day;
        }

        /// <summary>
        /// The method computes the difference between two Islamic 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 Islamic
        /// month of the first date.
        /// </param>
        /// <param name="yearA">The integer parameter gives the Islamic
        /// 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 Islamic
        /// month of the second date.
        /// </param>
        /// <param name="yearB">The integer parameter gives the Islamic
        /// 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 Islamic 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
        /// Islamic year.
        /// </param>
        /// <param name="year">An integer representing the Islamic year.
        /// </param>
        /// <returns>An integer value giving the number of the day in the
        /// Islamic year, counting from 1.
        /// </returns>
        public static int day_number(int day, int month, int year) {
                return date_difference(31, 12, year-1, day, month, year);
        }

        /// <summary>
        /// The method computes the days remaining in the given Islamic
        /// year from a Islamic 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
        /// Islamic year.
        /// </param>
        /// <param name="year">An integer representing the Islamic year.
        /// Non-positive values are allowed also.
        /// </param>
        /// <returns>An integer value giving the number of days remaining in
        /// the Islamic year.
        /// </returns>
        public static int days_remaining(int day, int month, int year) {
                return date_difference(day, month, year,31, 12, year);
        }
} // class CCHijriCalendar

internal class CCEastAsianLunisolarCalendar
{
        public static int fixed_from_dmy (int day, int month, int year)
        {
                /*
                int k = epoch - 1;
                k += 354 * (year - 1);
                k += CCMath.div (3+11*year, 30);
                k += (int) Math.Ceiling(29.53 * (double)(month-1));
                k += day;

                return k;
                */
                throw new Exception ("fixed_from_dmy");
        }

        public static int year_from_fixed (int date)
        {
                throw new Exception ("year_from_fixed");
        }

        public static void my_from_fixed(out int month, out int year, int date)
        {
                /*
                year = year_from_fixed (date);

                int m = 1+(int)System.Math.Ceiling(
                        ((double)(date-29-fixed_from_dmy(1,1,year)))/29.5);

                month = m < 12 ? m : 12;
                */
                throw new Exception ("my_from_fixed");
        }

        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;
                */
                throw new Exception ("dmy_from_fixed");
        }

        public static DateTime AddMonths (DateTime date, int months)
        {
                
                throw new Exception ("AddMonths");
        }

        public static DateTime AddYears (DateTime date, int years)
        {
                throw new Exception ("AddYears");
        }

        public static int GetDayOfMonth (DateTime date)
        {
                throw new Exception ("GetDayOfMonth");
        }

        public static int GetDayOfYear (DateTime date)
        {
                throw new Exception ("GetDayOfYear");
        }

        public static int GetDaysInMonth (int gyear, int month)
        {
                throw new Exception ("GetDaysInMonth");
        }

        public static int GetDaysInYear (int year)
        {
                throw new Exception ("GetDaysInYear");
        }

        public static int GetMonth (DateTime date)
        {
                throw new Exception ("GetMonth");
        }

        public static bool IsLeapMonth (int gyear, int month)
        {
                int goldenNumber = gyear % 19;

                bool chu = false;
                bool leap = false;
                double s = 0;
                for (int y = 0; y < goldenNumber; y++) {
                        for (int l = 0, m = 1; m <= month; m++) {
                                if (leap) {
                                        l += 30;
                                        leap = false;
                                        if (y == goldenNumber && m == month)
                                                return true;
                                } else {
                                        l += chu ? 30 : 29;
                                        chu = !chu;
                                        s += 30.44;
                                        if (s - l > 29)
                                                leap = true;
                                }
                        }
                }
                return false;
        }

        public static bool IsLeapYear (int gyear)
        {

                // FIXME: it is still wrong.
                int d = gyear % 19;
                switch (d) {
                case 0: case 3: case 6: case 9: case 11: case 14: case 17:
                        return true;
                default:
                        return false;
                }
                /*
                int goldenNumber = (gyear - 1900) % 19;
                int epact = 29;
                bool leap = false;
                while (goldenNumber-- >= 0) {
                        epact += 11;
                        leap = epact > 30;
                        if (epact > 30)
                                epact -= 30;
                }
                return leap;
                */
        }

        public static DateTime ToDateTime (int year, int month, int day, int hour, int minute, int second, int millisecond)
        {
                throw new Exception ("ToDateTime");
        }
}

/// <summary>
/// A class that supports the Gregorian based calendars with other eras
/// (e.g. <see cref="T:System.Gloablization.JapaneseCalendar"/>).
/// </summary>
[System.Serializable]
internal class CCGregorianEraHandler {
        /// <summary>
        /// A struct that represents a single era.
        /// </summary>
        [System.Serializable]
        struct Era {
                /// <summary>
                /// The integer number identifying the era.
                /// </summary>
                private int _nr;

                /// <value>
                /// A get-only property that gives the era integer number.
                /// </value>
                public int Nr { get { return _nr; } }

                /// <summary>This integer gives the first day of the era as
                /// fixed day number.
                /// </summary>
                private int _start; // inclusive
                /// <summary>
                /// This integer gives the gregorian year of the
                /// <see cref="M:_start"/> value.
                /// </summary>
                private int _gregorianYearStart;
                /// <summary>
                /// This integer gives the last day of the era as fixed day
                /// number.
                /// </summary>
                private int _end;   // inclusive        
                /// <summary>
                /// This integer gives the largest year number of this era.
                /// </summary>
                private int _maxYear;

                /// <summary>
                /// This constructor creates the era structure.
                /// </summary>
                /// <param name="nr">The integer number of the era.
                /// </param>
                /// <param name="start">The fixed day number defining the
                /// first day of the era.
                /// </param>
                /// <param name="end">The fixed day number that defines the
                /// last day of the era.
                /// </param>
                public Era(int nr, int start, int end) {
                        if (nr == 0)
                                throw new System.ArgumentException(
                                        "Era number shouldn't be zero.");
                        _nr = nr;
                        if (start > end) {
                                throw new System.ArgumentException(
                                        "Era should start before end.");
                        }
                        _start = start;
                        _end = end;

                        _gregorianYearStart =
                                CCGregorianCalendar.year_from_fixed(_start);
                        int gregorianYearEnd =
                                CCGregorianCalendar.year_from_fixed(_end);
                        _maxYear = gregorianYearEnd - _gregorianYearStart + 1;
                }

                /// <summary>
                /// This method computes the Gregorian year from the year
                /// of this era.
                /// </summary>
                /// <param name="year">An integer giving the year in the
                /// era.
                /// </param>
                /// <returns>
                /// The Gregorian year as integer.
                /// </returns>
                /// <exception cref="T:System.ArgumentOutOfRangeException">
                /// The exception is thrown if the year isn't valid in this
                /// era.
                /// </exception>
                public int GregorianYear(int year) {
                        if (year < 1 || year > _maxYear) {
                                System.IO.StringWriter sw = 
                                        new System.IO.StringWriter();
                                sw.Write(
                                        "Valid Values are between " +
                                        "{0} and {1}, inclusive.",
                                        1, _maxYear);
                                throw new System.ArgumentOutOfRangeException(
                                        "year", sw.ToString());
                        }
                        return year + _gregorianYearStart - 1;
                }

                /// <summary>
                /// This function checks wether the given fixed day number is
                /// ion the time span of the era.
                /// </summary>
                /// <param name="date">An integer giving the fixed day
                /// number.
                /// </param>
                /// <returns>A boolean: true if the argument is in the time
                /// span of the era.
                /// </returns>
                public bool Covers(int date) {
                        return _start <= date && date <= _end;
                }

                /// <summary>
                /// This function returns the year of the era and sets
                /// the era in an output parameter.
                /// </summary>
                /// <param name="era">An output parameter returning the
                /// era number.
                /// </param>
                /// <param name="date">An integer giving the fixed day
                /// number.
                /// </param>
                /// <returns>An integer giving the year of the era.
                /// </returns>
                /// <exception cref="T:System.ArgumentOutOfRangeException">
                /// The exception is thrown if date is outside of the time
                /// span of the era.
                /// </exception>
                public int EraYear(out int era, int date) {
                        if (!Covers(date))
                                throw new System.ArgumentOutOfRangeException(
                                        "date", 
                                        "Time was out of Era range.");
                        int gregorianYear =
                                CCGregorianCalendar.year_from_fixed(date);
                        era = _nr;
                        return gregorianYear - _gregorianYearStart + 1;
                }
        } // struct Era

        /// <summary>
        /// A private member storing the eras in a
        /// <see cref="T:System.Collections.SortedList"/>.
        /// </summary>
        private SortedList _Eras;

        /// <value>
        /// The property returns the era numbers as an array of integers.
        /// </value>
        public int[] Eras {
                get {
                        int[] a = new int[_Eras.Count];

                        for (int i = 0; i < _Eras.Count; i++) {
                                Era e = (Era)_Eras.GetByIndex(i);
                                a[i] = e.Nr;
                        }

                        return a;
                }
        }

        /// <summary>
        /// Constructor.
        /// </summary>
        public CCGregorianEraHandler() {
                _Eras = new SortedList();
        }

        /// <summary>
        /// Method adds an era to the GregorianEraHandler instance.
        /// </summary>
        /// <param name="nr">The integer number of the era.
        /// </param>
        /// <param name="rd_start">The fixed day number defining the
        /// first day of the era.
        /// </param>
        /// <param name="rd_end">The fixed day number that defines the
        /// last day of the era.
        /// </param>
        public void appendEra(int nr, int rd_start, int rd_end) {
                Era era = new Era(nr, rd_start, rd_end);
                _Eras[(System.Object)nr] = era;
        }
        /// <summary>
        /// Method adds a yet not-ended era to the GregorianEraHandler
        /// instance.
        /// </summary>
        /// <param name="nr">The integer number of the era.
        /// </param>
        /// <param name="rd_start">The fixed day number defining the
        /// first day of the era.
        /// </param>
        public void appendEra(int nr, int rd_start) {
                appendEra(nr, rd_start,
                        CCFixed.FromDateTime(DateTime.MaxValue));
        }

        /// <summary>
        /// This method computes the Gregorian year from the year
        /// of the given era.
        /// </summary>
        /// <param name="year">An integer giving the year in the
        /// era.
        /// </param>
        /// <param name="era">An integer giving the era number.
        /// </param>
        /// <returns>
        /// The Gregorian year as integer.
        /// </returns>
        /// <exception cref="T:System.ArgumentOutOfRangeException">
        /// The exception is thrown if the year isn't valid in this
        /// era.
        /// </exception>
        public int GregorianYear(int year, int era) {
                Era e = (Era)_Eras[(System.Object)era];
                return e.GregorianYear(year);
        }

        /// <summary>
        /// This function returns the year of the era and sets
        /// the era in an output parameter.
        /// </summary>
        /// <param name="era">An output parameter returning the
        /// era number.
        /// </param>
        /// <param name="date">An integer giving the fixed day
        /// number.
        /// </param>
        /// <returns>An integer giving the year of the era.
        /// </returns>
        /// <exception cref="T:System.ArgumentOutOfRangeException">
        /// The exception is thrown if the fixed day number is outside of the
        /// time spans of all eras.
        /// </exception>
        public int EraYear(out int era, int date)
        {
                IList list = _Eras.GetValueList();

                foreach (Era e in list) {
                        if (e.Covers(date))
                                return e.EraYear(out era, date);
                }

                throw new System.ArgumentOutOfRangeException("date",
                        "Time value was out of era range.");
        }

        /// <summary>
        /// The method checks whether a given
        /// <see cref="T:System.DateTime"/> is covered by any era.
        /// </summary>
        /// <param name="time">A 
        /// <see cref="T:System.DateTime"/> giving the date and time.
        /// </param>
        /// <exception cref="T:System.ArgumentOutOfRangeException">
        /// The exception is thrown if the argument isn't inside the time
        /// span of any era.
        /// </exception>
        public void CheckDateTime(System.DateTime time) {
                int date = CCFixed.FromDateTime(time);

                if (!ValidDate(date))
                        throw new System.ArgumentOutOfRangeException("time",
                                "Time value was out of era range.");
        }
                
        /// <summary>
        /// The method tests whether a given
        /// fixed day number is covered by any era.
        /// </summary>
        /// <param name="date">An integer representing the fixed day number.
        /// </param>
        /// <returns> A boolean is returned: true if the argument is inside
        /// the time span of one era; false otherwise.
        /// </returns>
        public bool ValidDate(int date) {
                IList list = _Eras.GetValueList();

                foreach (Era e in list) {
                        if (e.Covers(date))
                                return true;
                }

                return false;
        }

        /// <summary>
        /// The method tests, whether the era number does exist.
        /// </summary>
        /// <param name="era">An integer giving the era number.
        /// </param>
        /// <returns>A boole value: True if the era number does exist;
        /// false otherwise.
        /// </returns>
        public bool ValidEra(int era) {
                return _Eras.Contains((System.Object)era);
        }
} // class CCGregorianEraHandler


// FIXME: remove this class. It should be identical to CCGregorianEraHandler
[System.Serializable]
internal class CCEastAsianLunisolarEraHandler
{
        [Serializable]
        struct Era 
        {
                private int _nr; // era index

                public int Nr {
                        get { return _nr; }
                }

                private int _start; // inclusive
                private int _gregorianYearStart;
                private int _end;   // inclusive
                private int _maxYear;

                public Era (int nr, int start, int end)
                {
                        if (nr == 0)
                                throw new ArgumentException ("Era number shouldn't be zero.");
                        _nr = nr;
                        if (start > end)
                                throw new ArgumentException ("Era should start before end.");
                        _start = start;
                        _end = end;

                        _gregorianYearStart = CCGregorianCalendar.year_from_fixed (_start);
                        int gregorianYearEnd = CCGregorianCalendar.year_from_fixed (_end);
                        _maxYear = gregorianYearEnd - _gregorianYearStart + 1;
                }

                public int GregorianYear (int year) 
                {
                        if (year < 1 || year > _maxYear)
                                throw new ArgumentOutOfRangeException ("year", String.Format ("Valid Values are between {0} and {1}, inclusive.", 1, _maxYear));
                        return year + _gregorianYearStart - 1;
                }

                public bool Covers (int date) {
                        return _start <= date && date <= _end;
                }

                public int EraYear (out int era, int date) {
                        if (!Covers (date))
                                throw new ArgumentOutOfRangeException ("date", "Time was out of Era range.");
                        int gregorianYear = CCGregorianCalendar.year_from_fixed (date);
                        era = _nr;
                        return gregorianYear - _gregorianYearStart + 1;
                }
        }

        private SortedList _Eras;

        public int [] Eras 
        {
                get {
                        int[] a = new int [_Eras.Count];
                        for (int i = 0; i < _Eras.Count; i++) {
                                Era e = (Era) _Eras.GetByIndex (i);
                                a[i] = e.Nr;
                        }
                        return a;
                }
        }

        public CCEastAsianLunisolarEraHandler ()
        {
                _Eras = new SortedList ();
        }

        public void appendEra (int nr, int rd_start, int rd_end)
        {
                Era era = new Era (nr, rd_start, rd_end);
                _Eras [nr] = era;
        }

        public void appendEra (int nr, int rd_start)
        {
                appendEra (nr, rd_start, CCFixed.FromDateTime (DateTime.MaxValue));
        }

        public int GregorianYear (int year, int era)
        {
                Era e = (Era) _Eras [era];
                return e.GregorianYear (year);
        }

        public int EraYear (out int era, int date)
        {
                foreach (Era e in _Eras.Values)
                        if (e.Covers (date))
                                return e.EraYear (out era, date);

                throw new ArgumentOutOfRangeException ("date", "Time value was out of era range.");
        }

        public void CheckDateTime (DateTime time)
        {
                int date = CCFixed.FromDateTime (time);

                if (!ValidDate (date))
                        throw new ArgumentOutOfRangeException ("time", "Time value was out of era range.");
        }
                
        public bool ValidDate (int date)
        {
                foreach (Era e in _Eras.Values) {
                        if (e.Covers (date))
                                return true;
                }
                return false;
        }

        public bool ValidEra (int era)
        {
                return _Eras.Contains (era);
        }
}

} // namespace System.Globalization