netcore/System.Private.CoreLib/shared/System/Globalization/GregorianCalendarHelper.cs

   1 // Licensed to the .NET Foundation under one or more agreements.
   2 // The .NET Foundation licenses this file to you under the MIT license.
   3 // See the LICENSE file in the project root for more information.
   4
   5 using System;
   6 using System.Threading;
   7
   8 namespace System.Globalization
   9 {
  10     // Gregorian Calendars use Era Info
  11     internal class EraInfo
  12     {
  13         internal int era;          // The value of the era.
  14         internal long ticks;    // The time in ticks when the era starts
  15         internal int yearOffset;   // The offset to Gregorian year when the era starts.
  16                                    // Gregorian Year = Era Year + yearOffset
  17                                    // Era Year = Gregorian Year - yearOffset
  18         internal int minEraYear;   // Min year value in this era. Generally, this value is 1, but this may
  19                                    // be affected by the DateTime.MinValue;
  20         internal int maxEraYear;   // Max year value in this era. (== the year length of the era + 1)
  21
  22         internal string? eraName;    // The era name
  23         internal string? abbrevEraName;  // Abbreviated Era Name
  24         internal string? englishEraName; // English era name
  25
  26         internal EraInfo(int era, int startYear, int startMonth, int startDay, int yearOffset, int minEraYear, int maxEraYear)
  27         {
  28             this.era = era;
  29             this.yearOffset = yearOffset;
  30             this.minEraYear = minEraYear;
  31             this.maxEraYear = maxEraYear;
  32             this.ticks = new DateTime(startYear, startMonth, startDay).Ticks;
  33         }
  34
  35         internal EraInfo(int era, int startYear, int startMonth, int startDay, int yearOffset, int minEraYear, int maxEraYear,
  36                           string eraName, string abbrevEraName, string englishEraName)
  37         {
  38             this.era = era;
  39             this.yearOffset = yearOffset;
  40             this.minEraYear = minEraYear;
  41             this.maxEraYear = maxEraYear;
  42             this.ticks = new DateTime(startYear, startMonth, startDay).Ticks;
  43             this.eraName = eraName;
  44             this.abbrevEraName = abbrevEraName;
  45             this.englishEraName = englishEraName;
  46         }
  47     }
  48
  49     // This calendar recognizes two era values:
  50     // 0 CurrentEra (AD)
  51     // 1 BeforeCurrentEra (BC)
  52     internal class GregorianCalendarHelper
  53     {
  54         // 1 tick = 100ns = 10E-7 second
  55         // Number of ticks per time unit
  56         internal const long TicksPerMillisecond = 10000;
  57         internal const long TicksPerSecond = TicksPerMillisecond * 1000;
  58         internal const long TicksPerMinute = TicksPerSecond * 60;
  59         internal const long TicksPerHour = TicksPerMinute * 60;
  60         internal const long TicksPerDay = TicksPerHour * 24;
  61
  62         // Number of milliseconds per time unit
  63         internal const int MillisPerSecond = 1000;
  64         internal const int MillisPerMinute = MillisPerSecond * 60;
  65         internal const int MillisPerHour = MillisPerMinute * 60;
  66         internal const int MillisPerDay = MillisPerHour * 24;
  67
  68         // Number of days in a non-leap year
  69         internal const int DaysPerYear = 365;
  70         // Number of days in 4 years
  71         internal const int DaysPer4Years = DaysPerYear * 4 + 1;
  72         // Number of days in 100 years
  73         internal const int DaysPer100Years = DaysPer4Years * 25 - 1;
  74         // Number of days in 400 years
  75         internal const int DaysPer400Years = DaysPer100Years * 4 + 1;
  76
  77         // Number of days from 1/1/0001 to 1/1/10000
  78         internal const int DaysTo10000 = DaysPer400Years * 25 - 366;
  79
  80         internal const long MaxMillis = (long)DaysTo10000 * MillisPerDay;
  81
  82         internal const int DatePartYear = 0;
  83         internal const int DatePartDayOfYear = 1;
  84         internal const int DatePartMonth = 2;
  85         internal const int DatePartDay = 3;
  86
  87         //
  88         // This is the max Gregorian year can be represented by DateTime class.  The limitation
  89         // is derived from DateTime class.
  90         //
  91         internal int MaxYear => m_maxYear;
  92
  93         internal static readonly int[] DaysToMonth365 =
  94         {
  95             0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365
  96         };
  97
  98         internal static readonly int[] DaysToMonth366 =
  99         {
 100             0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366
 101         };
 102
 103         internal int m_maxYear = 9999;
 104         internal int m_minYear;
 105         internal Calendar m_Cal;
 106
 107         internal EraInfo[] m_EraInfo;
 108         internal int[]? m_eras = null;
 109
 110
 111         // Construct an instance of gregorian calendar.
 112         internal GregorianCalendarHelper(Calendar cal, EraInfo[] eraInfo)
 113         {
 114             m_Cal = cal;
 115             m_EraInfo = eraInfo;
 116             m_maxYear = m_EraInfo[0].maxEraYear;
 117             m_minYear = m_EraInfo[0].minEraYear; ;
 118         }
 119
 120         // EraInfo.yearOffset:  The offset to Gregorian year when the era starts. Gregorian Year = Era Year + yearOffset
 121         //                      Era Year = Gregorian Year - yearOffset
 122         // EraInfo.minEraYear:  Min year value in this era. Generally, this value is 1, but this may be affected by the DateTime.MinValue;
 123         // EraInfo.maxEraYear:  Max year value in this era. (== the year length of the era + 1)
 124         private int GetYearOffset(int year, int era, bool throwOnError)
 125         {
 126             if (year < 0)
 127             {
 128                 if (throwOnError)
 129                 {
 130                     throw new ArgumentOutOfRangeException(nameof(year), SR.ArgumentOutOfRange_NeedNonNegNum);
 131                 }
 132                 return -1;
 133             }
 134
 135             if (era == Calendar.CurrentEra)
 136             {
 137                 era = m_Cal.CurrentEraValue;
 138             }
 139
 140             for (int i = 0; i < m_EraInfo.Length; i++)
 141             {
 142                 if (era == m_EraInfo[i].era)
 143                 {
 144                     if (year >= m_EraInfo[i].minEraYear)
 145                     {
 146                         if (year <= m_EraInfo[i].maxEraYear)
 147                         {
 148                             return m_EraInfo[i].yearOffset;
 149                         }
 150                         else if (!LocalAppContextSwitches.EnforceJapaneseEraYearRanges)
 151                         {
 152                             // If we got the year number exceeding the era max year number, this still possible be valid as the date can be created before
 153                             // introducing new eras after the era we are checking. we'll loop on the eras after the era we have and ensure the year
 154                             // can exist in one of these eras. otherwise, we'll throw.
 155                             // Note, we always return the offset associated with the requested era.
 156                             //
 157                             // Here is some example:
 158                             // if we are getting the era number 4 (Heisei) and getting the year number 32. if the era 4 has year range from 1 to 31
 159                             // then year 32 exceeded the range of era 4 and we'll try to find out if the years difference (32 - 31 = 1) would lay in
 160                             // the subsequent eras (e.g era 5 and up)
 161
 162                             int remainingYears = year - m_EraInfo[i].maxEraYear;
 163
 164                             for (int j = i - 1; j >= 0; j--)
 165                             {
 166                                 if (remainingYears <= m_EraInfo[j].maxEraYear)
 167                                 {
 168                                     return m_EraInfo[i].yearOffset;
 169                                 }
 170                                 remainingYears -= m_EraInfo[j].maxEraYear;
 171                             }
 172                         }
 173                     }
 174
 175                     if (throwOnError)
 176                     {
 177                         throw new ArgumentOutOfRangeException(
 178                                     nameof(year),
 179                                     SR.Format(
 180                                         SR.ArgumentOutOfRange_Range,
 181                                         m_EraInfo[i].minEraYear,
 182                                         m_EraInfo[i].maxEraYear));
 183                     }
 184
 185                     break; // no need to iterate more on eras.
 186                 }
 187             }
 188
 189             if (throwOnError)
 190             {
 191                 throw new ArgumentOutOfRangeException(nameof(era), SR.ArgumentOutOfRange_InvalidEraValue);
 192             }
 193             return -1;
 194         }
 195
 196         /*=================================GetGregorianYear==========================
 197         **Action: Get the Gregorian year value for the specified year in an era.
 198         **Returns: The Gregorian year value.
 199         **Arguments:
 200         **      year    the year value in Japanese calendar
 201         **      era     the Japanese emperor era value.
 202         **Exceptions:
 203         **      ArgumentOutOfRangeException if year value is invalid or era value is invalid.
 204         ============================================================================*/
 205
 206         internal int GetGregorianYear(int year, int era)
 207         {
 208             return GetYearOffset(year, era, throwOnError: true) + year;
 209         }
 210
 211         internal bool IsValidYear(int year, int era)
 212         {
 213             return GetYearOffset(year, era, throwOnError: false) >= 0;
 214         }
 215
 216         // Returns a given date part of this DateTime. This method is used
 217         // to compute the year, day-of-year, month, or day part.
 218         internal virtual int GetDatePart(long ticks, int part)
 219         {
 220             CheckTicksRange(ticks);
 221             // n = number of days since 1/1/0001
 222             int n = (int)(ticks / TicksPerDay);
 223             // y400 = number of whole 400-year periods since 1/1/0001
 224             int y400 = n / DaysPer400Years;
 225             // n = day number within 400-year period
 226             n -= y400 * DaysPer400Years;
 227             // y100 = number of whole 100-year periods within 400-year period
 228             int y100 = n / DaysPer100Years;
 229             // Last 100-year period has an extra day, so decrement result if 4
 230             if (y100 == 4) y100 = 3;
 231             // n = day number within 100-year period
 232             n -= y100 * DaysPer100Years;
 233             // y4 = number of whole 4-year periods within 100-year period
 234             int y4 = n / DaysPer4Years;
 235             // n = day number within 4-year period
 236             n -= y4 * DaysPer4Years;
 237             // y1 = number of whole years within 4-year period
 238             int y1 = n / DaysPerYear;
 239             // Last year has an extra day, so decrement result if 4
 240             if (y1 == 4) y1 = 3;
 241             // If year was requested, compute and return it
 242             if (part == DatePartYear)
 243             {
 244                 return (y400 * 400 + y100 * 100 + y4 * 4 + y1 + 1);
 245             }
 246             // n = day number within year
 247             n -= y1 * DaysPerYear;
 248             // If day-of-year was requested, return it
 249             if (part == DatePartDayOfYear)
 250             {
 251                 return (n + 1);
 252             }
 253             // Leap year calculation looks different from IsLeapYear since y1, y4,
 254             // and y100 are relative to year 1, not year 0
 255             bool leapYear = (y1 == 3 && (y4 != 24 || y100 == 3));
 256             int[] days = leapYear ? DaysToMonth366 : DaysToMonth365;
 257             // All months have less than 32 days, so n >> 5 is a good conservative
 258             // estimate for the month
 259             int m = (n >> 5) + 1;
 260             // m = 1-based month number
 261             while (n >= days[m]) m++;
 262             // If month was requested, return it
 263             if (part == DatePartMonth) return (m);
 264             // Return 1-based day-of-month
 265             return (n - days[m - 1] + 1);
 266         }
 267
 268         /*=================================GetAbsoluteDate==========================
 269         **Action: Gets the absolute date for the given Gregorian date.  The absolute date means
 270         **       the number of days from January 1st, 1 A.D.
 271         **Returns:  the absolute date
 272         **Arguments:
 273         **      year    the Gregorian year
 274         **      month   the Gregorian month
 275         **      day     the day
 276         **Exceptions:
 277         **      ArgumentOutOfRangException  if year, month, day value is valid.
 278         **Note:
 279         **      This is an internal method used by DateToTicks() and the calculations of Hijri and Hebrew calendars.
 280         **      Number of Days in Prior Years (both common and leap years) +
 281         **      Number of Days in Prior Months of Current Year +
 282         **      Number of Days in Current Month
 283         **
 284         ============================================================================*/
 285
 286         internal static long GetAbsoluteDate(int year, int month, int day)
 287         {
 288             if (year >= 1 && year <= 9999 && month >= 1 && month <= 12)
 289             {
 290                 int[] days = ((year % 4 == 0 && (year % 100 != 0 || year % 400 == 0))) ? DaysToMonth366 : DaysToMonth365;
 291                 if (day >= 1 && (day <= days[month] - days[month - 1]))
 292                 {
 293                     int y = year - 1;
 294                     int absoluteDate = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
 295                     return (absoluteDate);
 296                 }
 297             }
 298             throw new ArgumentOutOfRangeException(null, SR.ArgumentOutOfRange_BadYearMonthDay);
 299         }
 300
 301         // Returns the tick count corresponding to the given year, month, and day.
 302         // Will check the if the parameters are valid.
 303         internal static long DateToTicks(int year, int month, int day)
 304         {
 305             return (GetAbsoluteDate(year, month, day) * TicksPerDay);
 306         }
 307
 308         // Return the tick count corresponding to the given hour, minute, second.
 309         // Will check the if the parameters are valid.
 310         internal static long TimeToTicks(int hour, int minute, int second, int millisecond)
 311         {
 312             //TimeSpan.TimeToTicks is a family access function which does no error checking, so
 313             //we need to put some error checking out here.
 314             if (hour >= 0 && hour < 24 && minute >= 0 && minute < 60 && second >= 0 && second < 60)
 315             {
 316                 if (millisecond < 0 || millisecond >= MillisPerSecond)
 317                 {
 318                     throw new ArgumentOutOfRangeException(
 319                                 nameof(millisecond),
 320                                 SR.Format(
 321                                     SR.ArgumentOutOfRange_Range,
 322                                     0,
 323                                     MillisPerSecond - 1));
 324                 }
 325                 return (InternalGlobalizationHelper.TimeToTicks(hour, minute, second) + millisecond * TicksPerMillisecond); ;
 326             }
 327             throw new ArgumentOutOfRangeException(null, SR.ArgumentOutOfRange_BadHourMinuteSecond);
 328         }
 329
 330
 331         internal void CheckTicksRange(long ticks)
 332         {
 333             if (ticks < m_Cal.MinSupportedDateTime.Ticks || ticks > m_Cal.MaxSupportedDateTime.Ticks)
 334             {
 335                 throw new ArgumentOutOfRangeException(
 336                             "time",
 337                             SR.Format(
 338                                 CultureInfo.InvariantCulture,
 339                                 SR.ArgumentOutOfRange_CalendarRange,
 340                                 m_Cal.MinSupportedDateTime,
 341                                 m_Cal.MaxSupportedDateTime));
 342             }
 343         }
 344
 345         // Returns the DateTime resulting from adding the given number of
 346         // months to the specified DateTime. The result is computed by incrementing
 347         // (or decrementing) the year and month parts of the specified DateTime by
 348         // value months, and, if required, adjusting the day part of the
 349         // resulting date downwards to the last day of the resulting month in the
 350         // resulting year. The time-of-day part of the result is the same as the
 351         // time-of-day part of the specified DateTime.
 352         //
 353         // In more precise terms, considering the specified DateTime to be of the
 354         // form y / m / d + t, where y is the
 355         // year, m is the month, d is the day, and t is the
 356         // time-of-day, the result is y1 / m1 / d1 + t,
 357         // where y1 and m1 are computed by adding value months
 358         // to y and m, and d1 is the largest value less than
 359         // or equal to d that denotes a valid day in month m1 of year
 360         // y1.
 361         //
 362         public DateTime AddMonths(DateTime time, int months)
 363         {
 364             if (months < -120000 || months > 120000)
 365             {
 366                 throw new ArgumentOutOfRangeException(
 367                             nameof(months),
 368                             SR.Format(
 369                                 SR.ArgumentOutOfRange_Range,
 370                                 -120000,
 371                                 120000));
 372             }
 373             CheckTicksRange(time.Ticks);
 374
 375             int y = GetDatePart(time.Ticks, DatePartYear);
 376             int m = GetDatePart(time.Ticks, DatePartMonth);
 377             int d = GetDatePart(time.Ticks, DatePartDay);
 378             int i = m - 1 + months;
 379             if (i >= 0)
 380             {
 381                 m = i % 12 + 1;
 382                 y += i / 12;
 383             }
 384             else
 385             {
 386                 m = 12 + (i + 1) % 12;
 387                 y += (i - 11) / 12;
 388             }
 389             int[] daysArray = (y % 4 == 0 && (y % 100 != 0 || y % 400 == 0)) ? DaysToMonth366 : DaysToMonth365;
 390             int days = (daysArray[m] - daysArray[m - 1]);
 391
 392             if (d > days)
 393             {
 394                 d = days;
 395             }
 396             long ticks = DateToTicks(y, m, d) + (time.Ticks % TicksPerDay);
 397             Calendar.CheckAddResult(ticks, m_Cal.MinSupportedDateTime, m_Cal.MaxSupportedDateTime);
 398             return (new DateTime(ticks));
 399         }
 400
 401         // Returns the DateTime resulting from adding the given number of
 402         // years to the specified DateTime. The result is computed by incrementing
 403         // (or decrementing) the year part of the specified DateTime by value
 404         // years. If the month and day of the specified DateTime is 2/29, and if the
 405         // resulting year is not a leap year, the month and day of the resulting
 406         // DateTime becomes 2/28. Otherwise, the month, day, and time-of-day
 407         // parts of the result are the same as those of the specified DateTime.
 408         //
 409         public DateTime AddYears(DateTime time, int years)
 410         {
 411             return (AddMonths(time, years * 12));
 412         }
 413
 414         // Returns the day-of-month part of the specified DateTime. The returned
 415         // value is an integer between 1 and 31.
 416         //
 417         public int GetDayOfMonth(DateTime time)
 418         {
 419             return (GetDatePart(time.Ticks, DatePartDay));
 420         }
 421
 422         // Returns the day-of-week part of the specified DateTime. The returned value
 423         // is an integer between 0 and 6, where 0 indicates Sunday, 1 indicates
 424         // Monday, 2 indicates Tuesday, 3 indicates Wednesday, 4 indicates
 425         // Thursday, 5 indicates Friday, and 6 indicates Saturday.
 426         //
 427         public DayOfWeek GetDayOfWeek(DateTime time)
 428         {
 429             CheckTicksRange(time.Ticks);
 430             return ((DayOfWeek)((time.Ticks / TicksPerDay + 1) % 7));
 431         }
 432
 433         // Returns the day-of-year part of the specified DateTime. The returned value
 434         // is an integer between 1 and 366.
 435         //
 436         public int GetDayOfYear(DateTime time)
 437         {
 438             return (GetDatePart(time.Ticks, DatePartDayOfYear));
 439         }
 440
 441         // Returns the number of days in the month given by the year and
 442         // month arguments.
 443         //
 444         public int GetDaysInMonth(int year, int month, int era)
 445         {
 446             //
 447             // Convert year/era value to Gregorain year value.
 448             //
 449             year = GetGregorianYear(year, era);
 450             if (month < 1 || month > 12)
 451             {
 452                 throw new ArgumentOutOfRangeException(nameof(month), SR.ArgumentOutOfRange_Month);
 453             }
 454             int[] days = ((year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)) ? DaysToMonth366 : DaysToMonth365);
 455             return (days[month] - days[month - 1]);
 456         }
 457
 458         // Returns the number of days in the year given by the year argument for the current era.
 459         //
 460
 461         public int GetDaysInYear(int year, int era)
 462         {
 463             //
 464             // Convert year/era value to Gregorain year value.
 465             //
 466             year = GetGregorianYear(year, era);
 467             return ((year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)) ? 366 : 365);
 468         }
 469
 470         // Returns the era for the specified DateTime value.
 471         public int GetEra(DateTime time)
 472         {
 473             long ticks = time.Ticks;
 474             // The assumption here is that m_EraInfo is listed in reverse order.
 475             for (int i = 0; i < m_EraInfo.Length; i++)
 476             {
 477                 if (ticks >= m_EraInfo[i].ticks)
 478                 {
 479                     return (m_EraInfo[i].era);
 480                 }
 481             }
 482             throw new ArgumentOutOfRangeException(nameof(time), SR.ArgumentOutOfRange_Era);
 483         }
 484
 485
 486         public int[] Eras
 487         {
 488             get
 489             {
 490                 if (m_eras == null)
 491                 {
 492                     m_eras = new int[m_EraInfo.Length];
 493                     for (int i = 0; i < m_EraInfo.Length; i++)
 494                     {
 495                         m_eras[i] = m_EraInfo[i].era;
 496                     }
 497                 }
 498                 return ((int[])m_eras.Clone());
 499             }
 500         }
 501
 502         // Returns the month part of the specified DateTime. The returned value is an
 503         // integer between 1 and 12.
 504         //
 505         public int GetMonth(DateTime time)
 506         {
 507             return (GetDatePart(time.Ticks, DatePartMonth));
 508         }
 509
 510         // Returns the number of months in the specified year and era.
 511         public int GetMonthsInYear(int year, int era)
 512         {
 513             GetGregorianYear(year, era);
 514             return 12;
 515         }
 516
 517         // Returns the year part of the specified DateTime. The returned value is an
 518         // integer between 1 and 9999.
 519         //
 520         public int GetYear(DateTime time)
 521         {
 522             long ticks = time.Ticks;
 523             int year = GetDatePart(ticks, DatePartYear);
 524             for (int i = 0; i < m_EraInfo.Length; i++)
 525             {
 526                 if (ticks >= m_EraInfo[i].ticks)
 527                 {
 528                     return (year - m_EraInfo[i].yearOffset);
 529                 }
 530             }
 531             throw new ArgumentException(SR.Argument_NoEra);
 532         }
 533
 534         // Returns the year that match the specified Gregorian year. The returned value is an
 535         // integer between 1 and 9999.
 536         //
 537         public int GetYear(int year, DateTime time)
 538         {
 539             long ticks = time.Ticks;
 540             for (int i = 0; i < m_EraInfo.Length; i++)
 541             {
 542                 // while calculating dates with JapaneseLuniSolarCalendar, we can run into cases right after the start of the era
 543                 // and still belong to the month which is started in previous era. Calculating equivalent calendar date will cause
 544                 // using the new era info which will have the year offset equal to the year we are calculating year = m_EraInfo[i].yearOffset
 545                 // which will end up with zero as calendar year.
 546                 // We should use the previous era info instead to get the right year number. Example of such date is Feb 2nd 1989
 547                 if (ticks >= m_EraInfo[i].ticks && year > m_EraInfo[i].yearOffset)
 548                 {
 549                     return (year - m_EraInfo[i].yearOffset);
 550                 }
 551             }
 552             throw new ArgumentException(SR.Argument_NoEra);
 553         }
 554
 555         // Checks whether a given day in the specified era is a leap day. This method returns true if
 556         // the date is a leap day, or false if not.
 557         //
 558         public bool IsLeapDay(int year, int month, int day, int era)
 559         {
 560             // year/month/era checking is done in GetDaysInMonth()
 561             if (day < 1 || day > GetDaysInMonth(year, month, era))
 562             {
 563                 throw new ArgumentOutOfRangeException(
 564                             nameof(day),
 565                             SR.Format(
 566                                 SR.ArgumentOutOfRange_Range,
 567                                 1,
 568                                 GetDaysInMonth(year, month, era)));
 569             }
 570
 571             if (!IsLeapYear(year, era))
 572             {
 573                 return (false);
 574             }
 575
 576             if (month == 2 && day == 29)
 577             {
 578                 return (true);
 579             }
 580
 581             return (false);
 582         }
 583
 584         // Returns  the leap month in a calendar year of the specified era. This method returns 0
 585         // if this calendar does not have leap month, or this year is not a leap year.
 586         //
 587         public int GetLeapMonth(int year, int era)
 588         {
 589             GetGregorianYear(year, era);
 590             return 0;
 591         }
 592
 593         // Checks whether a given month in the specified era is a leap month. This method returns true if
 594         // month is a leap month, or false if not.
 595         //
 596         public bool IsLeapMonth(int year, int month, int era)
 597         {
 598             year = GetGregorianYear(year, era);
 599             if (month < 1 || month > 12)
 600             {
 601                 throw new ArgumentOutOfRangeException(
 602                             nameof(month),
 603                             SR.Format(
 604                                 SR.ArgumentOutOfRange_Range,
 605                                 1,
 606                                 12));
 607             }
 608             return (false);
 609         }
 610
 611         // Checks whether a given year in the specified era is a leap year. This method returns true if
 612         // year is a leap year, or false if not.
 613         //
 614         public bool IsLeapYear(int year, int era)
 615         {
 616             year = GetGregorianYear(year, era);
 617             return (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
 618         }
 619
 620         // Returns the date and time converted to a DateTime value.  Throws an exception if the n-tuple is invalid.
 621         //
 622         public DateTime ToDateTime(int year, int month, int day, int hour, int minute, int second, int millisecond, int era)
 623         {
 624             year = GetGregorianYear(year, era);
 625             long ticks = DateToTicks(year, month, day) + TimeToTicks(hour, minute, second, millisecond);
 626             CheckTicksRange(ticks);
 627             return (new DateTime(ticks));
 628         }
 629
 630         public virtual int GetWeekOfYear(DateTime time, CalendarWeekRule rule, DayOfWeek firstDayOfWeek)
 631         {
 632             CheckTicksRange(time.Ticks);
 633             // Use GregorianCalendar to get around the problem that the implmentation in Calendar.GetWeekOfYear()
 634             // can call GetYear() that exceeds the supported range of the Gregorian-based calendars.
 635             return (GregorianCalendar.GetDefaultInstance().GetWeekOfYear(time, rule, firstDayOfWeek));
 636         }
 637
 638
 639         public int ToFourDigitYear(int year, int twoDigitYearMax)
 640         {
 641             if (year < 0)
 642             {
 643                 throw new ArgumentOutOfRangeException(nameof(year),
 644                     SR.ArgumentOutOfRange_NeedPosNum);
 645             }
 646
 647             if (year < 100)
 648             {
 649                 int y = year % 100;
 650                 return ((twoDigitYearMax / 100 - (y > twoDigitYearMax % 100 ? 1 : 0)) * 100 + y);
 651             }
 652
 653             if (year < m_minYear || year > m_maxYear)
 654             {
 655                 throw new ArgumentOutOfRangeException(
 656                             nameof(year),
 657                             SR.Format(SR.ArgumentOutOfRange_Range, m_minYear, m_maxYear));
 658             }
 659             // If the year value is above 100, just return the year value.  Don't have to do
 660             // the TwoDigitYearMax comparison.
 661             return (year);
 662         }
 663     }
 664 }