88 lines
3.1 KiB
C++
88 lines
3.1 KiB
C++
/*
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**********************************************************************
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* Copyright (c) 2003, International Business Machines
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* Corporation and others. All Rights Reserved.
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**********************************************************************
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* Author: Alan Liu
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* Created: September 2 2003
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* Since: ICU 2.8
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**********************************************************************
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*/
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#include "gregoimp.h"
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#include "unicode/ucal.h"
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int32_t Math::floorDivide(int32_t numerator, int32_t denominator) {
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return (numerator >= 0) ?
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numerator / denominator : ((numerator + 1) / denominator) - 1;
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}
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int32_t Math::floorDivide(double numerator, int32_t denominator,
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int32_t& remainder) {
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double quotient;
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quotient = uprv_floor(numerator / denominator);
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remainder = (int32_t) (numerator - (quotient * denominator));
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return (int32_t) quotient;
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}
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const int32_t JULIAN_1_CE = 1721426; // January 1, 1 CE Gregorian
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const int32_t JULIAN_1970_CE = 2440588; // January 1, 1970 CE Gregorian
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const int16_t Grego::DAYS_BEFORE[24] =
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{0,31,59,90,120,151,181,212,243,273,304,334,
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0,31,60,91,121,152,182,213,244,274,305,335};
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const int8_t Grego::MONTH_LENGTH[24] =
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{31,28,31,30,31,30,31,31,30,31,30,31,
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31,29,31,30,31,30,31,31,30,31,30,31};
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double Grego::fieldsToDay(int32_t year, int32_t month, int32_t dom) {
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int32_t y = year - 1;
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double julian = 365 * y + Math::floorDivide(y, 4) + (JULIAN_1_CE - 3) + // Julian cal
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Math::floorDivide(y, 400) - Math::floorDivide(y, 100) + 2 + // => Gregorian cal
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DAYS_BEFORE[month + (isLeapYear(year) ? 12 : 0)] + dom; // => month/dom
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return julian - JULIAN_1970_CE; // JD => epoch day
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}
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void Grego::dayToFields(double day, int32_t& year, int32_t& month,
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int32_t& dom, int32_t& dow) {
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int32_t doy;
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// Convert from 1970 CE epoch to 1 CE epoch (Gregorian calendar)
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day += JULIAN_1970_CE - JULIAN_1_CE;
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// Convert from the day number to the multiple radix
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// representation. We use 400-year, 100-year, and 4-year cycles.
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// For example, the 4-year cycle has 4 years + 1 leap day; giving
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// 1461 == 365*4 + 1 days.
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int32_t n400 = Math::floorDivide(day, 146097, doy); // 400-year cycle length
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int32_t n100 = Math::floorDivide(doy, 36524, doy); // 100-year cycle length
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int32_t n4 = Math::floorDivide(doy, 1461, doy); // 4-year cycle length
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int32_t n1 = Math::floorDivide(doy, 365, doy);
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year = 400*n400 + 100*n100 + 4*n4 + n1;
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if (n100 == 4 || n1 == 4) {
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doy = 365; // Dec 31 at end of 4- or 400-year cycle
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} else {
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++year;
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}
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UBool isLeap = isLeapYear(year);
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// Gregorian day zero is a Monday.
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dow = (int32_t) uprv_fmod(day + 1, 7);
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dow += (dow < 0) ? (UCAL_SUNDAY + 7) : UCAL_SUNDAY;
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// Common Julian/Gregorian calculation
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int32_t correction = 0;
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int32_t march1 = isLeap ? 60 : 59; // zero-based DOY for March 1
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if (doy >= march1) {
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correction = isLeap ? 1 : 2;
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}
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month = (12 * (doy + correction) + 6) / 367; // zero-based month
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dom = doy - DAYS_BEFORE[month + (isLeap ? 12 : 0)] + 1; // one-based DOM
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}
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//eof
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