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+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+ **********************************************************************
+ * Copyright (c) 2003-2008, International Business Machines
+ * Corporation and others.  All Rights Reserved.
+ **********************************************************************
+ * Author: Alan Liu
+ * Created: September 2 2003
+ * Since: ICU 2.8
+ **********************************************************************
+ */
+
+#ifndef GREGOIMP_H
+#define GREGOIMP_H
+#include "unicode/utypes.h"
+#if !UCONFIG_NO_FORMATTING
+
+#include "unicode/ures.h"
+#include "unicode/locid.h"
+#include "putilimp.h"
+
+U_NAMESPACE_BEGIN
+
+/**
+ * A utility class providing mathematical functions used by time zone
+ * and calendar code.  Do not instantiate.  Formerly just named 'Math'.
+ * @internal
+ */
+class ClockMath {
+ public:
+    /**
+     * Divide two integers, returning the floor of the quotient.
+     * Unlike the built-in division, this is mathematically
+     * well-behaved.  E.g., <code>-1/4</code> => 0 but
+     * <code>floorDivide(-1,4)</code> => -1.
+     * @param numerator the numerator
+     * @param denominator a divisor which must be != 0
+     * @return the floor of the quotient
+     */
+    static int32_t floorDivide(int32_t numerator, int32_t denominator);
+
+    /**
+     * Divide two integers, returning the floor of the quotient.
+     * Unlike the built-in division, this is mathematically
+     * well-behaved.  E.g., <code>-1/4</code> => 0 but
+     * <code>floorDivide(-1,4)</code> => -1.
+     * @param numerator the numerator
+     * @param denominator a divisor which must be != 0
+     * @return the floor of the quotient
+     */
+    static int64_t floorDivide(int64_t numerator, int64_t denominator);
+
+    /**
+     * Divide two numbers, returning the floor of the quotient.
+     * Unlike the built-in division, this is mathematically
+     * well-behaved.  E.g., <code>-1/4</code> => 0 but
+     * <code>floorDivide(-1,4)</code> => -1.
+     * @param numerator the numerator
+     * @param denominator a divisor which must be != 0
+     * @return the floor of the quotient
+     */
+    static inline double floorDivide(double numerator, double denominator);
+
+    /**
+     * Divide two numbers, returning the floor of the quotient and
+     * the modulus remainder.  Unlike the built-in division, this is
+     * mathematically well-behaved.  E.g., <code>-1/4</code> => 0 and
+     * <code>-1%4</code> => -1, but <code>floorDivide(-1,4)</code> =>
+     * -1 with <code>remainder</code> => 3.  NOTE: If numerator is
+     * too large, the returned quotient may overflow.
+     * @param numerator the numerator
+     * @param denominator a divisor which must be != 0
+     * @param remainder output parameter to receive the
+     * remainder. Unlike <code>numerator % denominator</code>, this
+     * will always be non-negative, in the half-open range <code>[0,
+     * |denominator|)</code>.
+     * @return the floor of the quotient
+     */
+    static int32_t floorDivide(double numerator, int32_t denominator,
+                               int32_t* remainder);
+
+    /**
+     * For a positive divisor, return the quotient and remainder
+     * such that dividend = quotient*divisor + remainder and
+     * 0 <= remainder < divisor.
+     *
+     * Works around edge-case bugs.  Handles pathological input
+     * (dividend >> divisor) reasonably.
+     *
+     * Calling with a divisor <= 0 is disallowed.
+     */
+    static double floorDivide(double dividend, double divisor,
+                              double* remainder);
+};
+
+// Useful millisecond constants
+#define kOneDay    (1.0 * U_MILLIS_PER_DAY)       //  86,400,000
+#define kOneHour   (60*60*1000)
+#define kOneMinute 60000
+#define kOneSecond 1000
+#define kOneMillisecond  1
+#define kOneWeek   (7.0 * kOneDay) // 604,800,000
+
+// Epoch constants
+#define kJan1_1JulianDay  1721426 // January 1, year 1 (Gregorian)
+
+#define kEpochStartAsJulianDay  2440588 // January 1, 1970 (Gregorian)
+
+#define kEpochYear              1970
+
+
+#define kEarliestViableMillis  -185331720384000000.0  // minimum representable by julian day  -1e17
+
+#define kLatestViableMillis     185753453990400000.0  // max representable by julian day      +1e17
+
+/**
+ * The minimum supported Julian day.  This value is equivalent to
+ * MIN_MILLIS.
+ */
+#define MIN_JULIAN (-0x7F000000)
+
+/**
+ * The minimum supported epoch milliseconds.  This value is equivalent
+ * to MIN_JULIAN.
+ */
+#define MIN_MILLIS ((MIN_JULIAN - kEpochStartAsJulianDay) * kOneDay)
+
+/**
+ * The maximum supported Julian day.  This value is equivalent to
+ * MAX_MILLIS.
+ */
+#define MAX_JULIAN (+0x7F000000)
+
+/**
+ * The maximum supported epoch milliseconds.  This value is equivalent
+ * to MAX_JULIAN.
+ */
+#define MAX_MILLIS ((MAX_JULIAN - kEpochStartAsJulianDay) * kOneDay)
+
+/**
+ * A utility class providing proleptic Gregorian calendar functions
+ * used by time zone and calendar code.  Do not instantiate.
+ *
+ * Note:  Unlike GregorianCalendar, all computations performed by this
+ * class occur in the pure proleptic GregorianCalendar.
+ */
+class Grego {
+ public:
+    /**
+     * Return true if the given year is a leap year.
+     * @param year Gregorian year, with 0 == 1 BCE, -1 == 2 BCE, etc.
+     * @return true if the year is a leap year
+     */
+    static inline UBool isLeapYear(int32_t year);
+
+    /**
+     * Return the number of days in the given month.
+     * @param year Gregorian year, with 0 == 1 BCE, -1 == 2 BCE, etc.
+     * @param month 0-based month, with 0==Jan
+     * @return the number of days in the given month
+     */
+    static inline int8_t monthLength(int32_t year, int32_t month);
+
+    /**
+     * Return the length of a previous month of the Gregorian calendar.
+     * @param y the extended year
+     * @param m the 0-based month number
+     * @return the number of days in the month previous to the given month
+     */
+    static inline int8_t previousMonthLength(int y, int m);
+
+    /**
+     * Convert a year, month, and day-of-month, given in the proleptic
+     * Gregorian calendar, to 1970 epoch days.
+     * @param year Gregorian year, with 0 == 1 BCE, -1 == 2 BCE, etc.
+     * @param month 0-based month, with 0==Jan
+     * @param dom 1-based day of month
+     * @return the day number, with day 0 == Jan 1 1970
+     */
+    static double fieldsToDay(int32_t year, int32_t month, int32_t dom);
+    
+    /**
+     * Convert a 1970-epoch day number to proleptic Gregorian year,
+     * month, day-of-month, and day-of-week.
+     * @param day 1970-epoch day (integral value)
+     * @param year output parameter to receive year
+     * @param month output parameter to receive month (0-based, 0==Jan)
+     * @param dom output parameter to receive day-of-month (1-based)
+     * @param dow output parameter to receive day-of-week (1-based, 1==Sun)
+     * @param doy output parameter to receive day-of-year (1-based)
+     */
+    static void dayToFields(double day, int32_t& year, int32_t& month,
+                            int32_t& dom, int32_t& dow, int32_t& doy);
+
+    /**
+     * Convert a 1970-epoch day number to proleptic Gregorian year,
+     * month, day-of-month, and day-of-week.
+     * @param day 1970-epoch day (integral value)
+     * @param year output parameter to receive year
+     * @param month output parameter to receive month (0-based, 0==Jan)
+     * @param dom output parameter to receive day-of-month (1-based)
+     * @param dow output parameter to receive day-of-week (1-based, 1==Sun)
+     */
+    static inline void dayToFields(double day, int32_t& year, int32_t& month,
+                                   int32_t& dom, int32_t& dow);
+
+    /**
+     * Convert a 1970-epoch milliseconds to proleptic Gregorian year,
+     * month, day-of-month, and day-of-week, day of year and millis-in-day.
+     * @param time 1970-epoch milliseconds
+     * @param year output parameter to receive year
+     * @param month output parameter to receive month (0-based, 0==Jan)
+     * @param dom output parameter to receive day-of-month (1-based)
+     * @param dow output parameter to receive day-of-week (1-based, 1==Sun)
+     * @param doy output parameter to receive day-of-year (1-based)
+     * @param mid output parameter to receive millis-in-day
+     */
+    static void timeToFields(UDate time, int32_t& year, int32_t& month,
+                            int32_t& dom, int32_t& dow, int32_t& doy, int32_t& mid);
+
+    /**
+     * Return the day of week on the 1970-epoch day
+     * @param day the 1970-epoch day (integral value)
+     * @return the day of week
+     */
+    static int32_t dayOfWeek(double day);
+
+    /**
+     * Returns the ordinal number for the specified day of week within the month.
+     * The valid return value is 1, 2, 3, 4 or -1.
+     * @param year Gregorian year, with 0 == 1 BCE, -1 == 2 BCE, etc.
+     * @param month 0-based month, with 0==Jan
+     * @param dom 1-based day of month
+     * @return The ordinal number for the specified day of week within the month
+     */
+    static int32_t dayOfWeekInMonth(int32_t year, int32_t month, int32_t dom);
+
+    /**
+     * Converts Julian day to time as milliseconds.
+     * @param julian the given Julian day number.
+     * @return time as milliseconds.
+     * @internal
+     */
+    static inline double julianDayToMillis(int32_t julian);
+
+    /**
+     * Converts time as milliseconds to Julian day.
+     * @param millis the given milliseconds.
+     * @return the Julian day number.
+     * @internal
+     */
+    static inline int32_t millisToJulianDay(double millis);
+
+    /** 
+     * Calculates the Gregorian day shift value for an extended year.
+     * @param eyear Extended year 
+     * @returns number of days to ADD to Julian in order to convert from J->G
+     */
+    static inline int32_t gregorianShift(int32_t eyear);
+
+ private:
+    static const int16_t DAYS_BEFORE[24];
+    static const int8_t MONTH_LENGTH[24];
+};
+
+inline double ClockMath::floorDivide(double numerator, double denominator) {
+    return uprv_floor(numerator / denominator);
+}
+
+inline UBool Grego::isLeapYear(int32_t year) {
+    // year&0x3 == year%4
+    return ((year&0x3) == 0) && ((year%100 != 0) || (year%400 == 0));
+}
+
+inline int8_t
+Grego::monthLength(int32_t year, int32_t month) {
+    return MONTH_LENGTH[month + (isLeapYear(year) ? 12 : 0)];
+}
+
+inline int8_t
+Grego::previousMonthLength(int y, int m) {
+  return (m > 0) ? monthLength(y, m-1) : 31;
+}
+
+inline void Grego::dayToFields(double day, int32_t& year, int32_t& month,
+                               int32_t& dom, int32_t& dow) {
+  int32_t doy_unused;
+  dayToFields(day,year,month,dom,dow,doy_unused);
+}
+
+inline double Grego::julianDayToMillis(int32_t julian)
+{
+  return (julian - kEpochStartAsJulianDay) * kOneDay;
+}
+
+inline int32_t Grego::millisToJulianDay(double millis) {
+  return (int32_t) (kEpochStartAsJulianDay + ClockMath::floorDivide(millis, (double)kOneDay));
+}
+
+inline int32_t Grego::gregorianShift(int32_t eyear) {
+  int64_t y = (int64_t)eyear-1;
+  int32_t gregShift = static_cast<int32_t>(ClockMath::floorDivide(y, (int64_t)400) - ClockMath::floorDivide(y, (int64_t)100) + 2);
+  return gregShift;
+}
+
+U_NAMESPACE_END
+
+#endif // !UCONFIG_NO_FORMATTING
+#endif // GREGOIMP_H
+
+//eof