| /* $selId: gregor.c,v 2.0 1995/10/24 01:13:06 lees Exp $ | |
| * Copyright 1993-1995, Scott E. Lee, all rights reserved. | |
| * Permission granted to use, copy, modify, distribute and sell so long as | |
| * the above copyright and this permission statement are retained in all | |
| * copies. THERE IS NO WARRANTY - USE AT YOUR OWN RISK. | |
| */ | |
| /************************************************************************** | |
| * | |
| * These are the externally visible components of this file: | |
| * | |
| * void | |
| * SdnToGregorian( | |
| * long int sdn, | |
| * int *pYear, | |
| * int *pMonth, | |
| * int *pDay); | |
| * | |
| * Convert a SDN to a Gregorian calendar date. If the input SDN is less | |
| * than 1, the three output values will all be set to zero, otherwise | |
| * *pYear will be >= -4714 and != 0; *pMonth will be in the range 1 to 12 | |
| * inclusive; *pDay will be in the range 1 to 31 inclusive. | |
| * | |
| * long int | |
| * GregorianToSdn( | |
| * int inputYear, | |
| * int inputMonth, | |
| * int inputDay); | |
| * | |
| * Convert a Gregorian calendar date to a SDN. Zero is returned when the | |
| * input date is detected as invalid or out of the supported range. The | |
| * return value will be > 0 for all valid, supported dates, but there are | |
| * some invalid dates that will return a positive value. To verify that a | |
| * date is valid, convert it to SDN and then back and compare with the | |
| * original. | |
| * | |
| * char *MonthNameShort[13]; | |
| * | |
| * Convert a Gregorian month number (1 to 12) to the abbreviated (three | |
| * character) name of the Gregorian month (null terminated). An index of | |
| * zero will return a zero length string. | |
| * | |
| * char *MonthNameLong[13]; | |
| * | |
| * Convert a Gregorian month number (1 to 12) to the name of the Gregorian | |
| * month (null terminated). An index of zero will return a zero length | |
| * string. | |
| * | |
| * VALID RANGE | |
| * | |
| * 4714 B.C. to at least 10000 A.D. | |
| * | |
| * Although this software can handle dates all the way back to 4714 | |
| * B.C., such use may not be meaningful. The Gregorian calendar was | |
| * not instituted until October 15, 1582 (or October 5, 1582 in the | |
| * Julian calendar). Some countries did not accept it until much | |
| * later. For example, Britain converted in 1752, The USSR in 1918 and | |
| * Greece in 1923. Most European countries used the Julian calendar | |
| * prior to the Gregorian. | |
| * | |
| * CALENDAR OVERVIEW | |
| * | |
| * The Gregorian calendar is a modified version of the Julian calendar. | |
| * The only difference being the specification of leap years. The | |
| * Julian calendar specifies that every year that is a multiple of 4 | |
| * will be a leap year. This leads to a year that is 365.25 days long, | |
| * but the current accepted value for the tropical year is 365.242199 | |
| * days. | |
| * | |
| * To correct this error in the length of the year and to bring the | |
| * vernal equinox back to March 21, Pope Gregory XIII issued a papal | |
| * bull declaring that Thursday October 4, 1582 would be followed by | |
| * Friday October 15, 1582 and that centennial years would only be a | |
| * leap year if they were a multiple of 400. This shortened the year | |
| * by 3 days per 400 years, giving a year of 365.2425 days. | |
| * | |
| * Another recently proposed change in the leap year rule is to make | |
| * years that are multiples of 4000 not a leap year, but this has never | |
| * been officially accepted and this rule is not implemented in these | |
| * algorithms. | |
| * | |
| * ALGORITHMS | |
| * | |
| * The calculations are based on three different cycles: a 400 year | |
| * cycle of leap years, a 4 year cycle of leap years and a 5 month | |
| * cycle of month lengths. | |
| * | |
| * The 5 month cycle is used to account for the varying lengths of | |
| * months. You will notice that the lengths alternate between 30 | |
| * and 31 days, except for three anomalies: both July and August | |
| * have 31 days, both December and January have 31, and February | |
| * is less than 30. Starting with March, the lengths are in a | |
| * cycle of 5 months (31, 30, 31, 30, 31): | |
| * | |
| * Mar 31 days \ | |
| * Apr 30 days | | |
| * May 31 days > First cycle | |
| * Jun 30 days | | |
| * Jul 31 days / | |
| * | |
| * Aug 31 days \ | |
| * Sep 30 days | | |
| * Oct 31 days > Second cycle | |
| * Nov 30 days | | |
| * Dec 31 days / | |
| * | |
| * Jan 31 days \ | |
| * Feb 28/9 days | | |
| * > Third cycle (incomplete) | |
| * | |
| * For this reason the calculations (internally) assume that the | |
| * year starts with March 1. | |
| * | |
| * TESTING | |
| * | |
| * This algorithm has been tested from the year 4714 B.C. to 10000 | |
| * A.D. The source code of the verification program is included in | |
| * this package. | |
| * | |
| * REFERENCES | |
| * | |
| * Conversions Between Calendar Date and Julian Day Number by Robert J. | |
| * Tantzen, Communications of the Association for Computing Machinery | |
| * August 1963. (Also published in Collected Algorithms from CACM, | |
| * algorithm number 199). | |
| * | |
| **************************************************************************/ | |
| void SdnToGregorian( | |
| zend_long sdn, | |
| int *pYear, | |
| int *pMonth, | |
| int *pDay) | |
| { | |
| int century; | |
| int year; | |
| int month; | |
| int day; | |
| zend_long temp; | |
| int dayOfYear; | |
| if (sdn <= 0 || | |
| sdn > (ZEND_LONG_MAX - 4 * GREGOR_SDN_OFFSET) / 4) { | |
| goto fail; | |
| } | |
| temp = (sdn + GREGOR_SDN_OFFSET) * 4 - 1; | |
| if (temp < 0 || (temp / DAYS_PER_400_YEARS) > INT_MAX) { | |
| goto fail; | |
| } | |
| /* Calculate the century (year/100). */ | |
| century = temp / DAYS_PER_400_YEARS; | |
| /* Calculate the year and day of year (1 <= dayOfYear <= 366). */ | |
| temp = ((temp % DAYS_PER_400_YEARS) / 4) * 4 + 3; | |
| if (century > ((INT_MAX / 100) - (temp / DAYS_PER_4_YEARS))) { | |
| goto fail; | |
| } | |
| year = (century * 100) + (temp / DAYS_PER_4_YEARS); | |
| dayOfYear = (temp % DAYS_PER_4_YEARS) / 4 + 1; | |
| /* Calculate the month and day of month. */ | |
| temp = dayOfYear * 5 - 3; | |
| month = temp / DAYS_PER_5_MONTHS; | |
| day = (temp % DAYS_PER_5_MONTHS) / 5 + 1; | |
| /* Convert to the normal beginning of the year. */ | |
| if (month < 10) { | |
| month += 3; | |
| } else { | |
| year += 1; | |
| month -= 9; | |
| } | |
| /* Adjust to the B.C./A.D. type numbering. */ | |
| year -= 4800; | |
| if (year <= 0) | |
| year--; | |
| *pYear = year; | |
| *pMonth = month; | |
| *pDay = day; | |
| return; | |
| fail: | |
| *pYear = 0; | |
| *pMonth = 0; | |
| *pDay = 0; | |
| } | |
| zend_long GregorianToSdn( | |
| int inputYear, | |
| int inputMonth, | |
| int inputDay) | |
| { | |
| zend_long year; | |
| int month; | |
| /* check for invalid dates */ | |
| if (inputYear == 0 || inputYear < -4714 || | |
| inputMonth <= 0 || inputMonth > 12 || | |
| inputDay <= 0 || inputDay > 31) { | |
| return (0); | |
| } | |
| /* check for dates before SDN 1 (Nov 25, 4714 B.C.) */ | |
| if (inputYear == -4714) { | |
| if (inputMonth < 11) { | |
| return (0); | |
| } | |
| if (inputMonth == 11 && inputDay < 25) { | |
| return (0); | |
| } | |
| } | |
| /* Make year always a positive number. */ | |
| if (inputYear < 0) { | |
| year = inputYear + 4801; | |
| } else { | |
| year = inputYear + 4800; | |
| } | |
| /* Adjust the start of the year. */ | |
| if (inputMonth > 2) { | |
| month = inputMonth - 3; | |
| } else { | |
| month = inputMonth + 9; | |
| year--; | |
| } | |
| return (((year / 100) * DAYS_PER_400_YEARS) / 4 | |
| + ((year % 100) * DAYS_PER_4_YEARS) / 4 | |
| + (month * DAYS_PER_5_MONTHS + 2) / 5 | |
| + inputDay | |
| - GREGOR_SDN_OFFSET); | |
| } | |
| const char * const MonthNameShort[13] = | |
| { | |
| "", | |
| "Jan", | |
| "Feb", | |
| "Mar", | |
| "Apr", | |
| "May", | |
| "Jun", | |
| "Jul", | |
| "Aug", | |
| "Sep", | |
| "Oct", | |
| "Nov", | |
| "Dec" | |
| }; | |
| const char * const MonthNameLong[13] = | |
| { | |
| "", | |
| "January", | |
| "February", | |
| "March", | |
| "April", | |
| "May", | |
| "June", | |
| "July", | |
| "August", | |
| "September", | |
| "October", | |
| "November", | |
| "December" | |
| }; | |