Source/WTF/wtf/DateMath.h - WebKit - Git at Google

 /*
  * Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
  * Copyright (C) 2006-2020 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Research In Motion Limited. All rights reserved.
  *
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
  * The contents of this file are subject to the Mozilla Public License Version
  * 1.1 (the "License"); you may not use this file except in compliance with
  * the License. You may obtain a copy of the License at
  * http://www.mozilla.org/MPL/
  *
  * Software distributed under the License is distributed on an "AS IS" basis,
  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  * for the specific language governing rights and limitations under the
  * License.
  *
  * The Original Code is Mozilla Communicator client code, released
  * March 31, 1998.
  *
  * The Initial Developer of the Original Code is
  * Netscape Communications Corporation.
  * Portions created by the Initial Developer are Copyright (C) 1998
  * the Initial Developer. All Rights Reserved.
  *
  * Contributor(s):
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either of the GNU General Public License Version 2 or later (the "GPL"),
  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  * in which case the provisions of the GPL or the LGPL are applicable instead
  * of those above. If you wish to allow use of your version of this file only
  * under the terms of either the GPL or the LGPL, and not to allow others to
  * use your version of this file under the terms of the MPL, indicate your
  * decision by deleting the provisions above and replace them with the notice
  * and other provisions required by the GPL or the LGPL. If you do not delete
  * the provisions above, a recipient may use your version of this file under
  * the terms of any one of the MPL, the GPL or the LGPL.
  *
  */

 #pragma once

 #include <math.h>
 #include <stdint.h>
 #include <string.h>
 #include <time.h>
 #include <wtf/WallTime.h>
 #include <wtf/text/WTFString.h>

 namespace WTF {

 enum TimeType {
     UTCTime = 0,
     LocalTime
 };

 struct LocalTimeOffset {
     WTF_MAKE_STRUCT_FAST_ALLOCATED;

     LocalTimeOffset() = default;
     constexpr LocalTimeOffset(bool isDST, int offset)
         : isDST(isDST)
         , offset(offset)
     {
     }

     bool operator==(const LocalTimeOffset& other) const
     {
         return isDST == other.isDST && offset == other.offset;
     }

     bool operator!=(const LocalTimeOffset& other) const
     {
         return isDST != other.isDST || offset != other.offset;
     }

     bool isDST { false };
     int offset { 0 };
 };

 void initializeDates();
 int equivalentYearForDST(int year);

 // Not really math related, but this is currently the only shared place to put these.
 WTF_EXPORT_PRIVATE double parseES5DateFromNullTerminatedCharacters(const char* dateString, bool& isLocalTime);
 WTF_EXPORT_PRIVATE double parseDateFromNullTerminatedCharacters(const char* dateString);
 WTF_EXPORT_PRIVATE double parseDateFromNullTerminatedCharacters(const char* dateString, bool& isLocalTime);
 // dayOfWeek: [0, 6] 0 being Monday, day: [1, 31], month: [0, 11], year: ex: 2011, hours: [0, 23], minutes: [0, 59], seconds: [0, 59], utcOffset: [-720,720].
 WTF_EXPORT_PRIVATE String makeRFC2822DateString(unsigned dayOfWeek, unsigned day, unsigned month, unsigned year, unsigned hours, unsigned minutes, unsigned seconds, int utcOffset);

 inline double jsCurrentTime()
 {
     // JavaScript doesn't recognize fractions of a millisecond.
     return floor(WallTime::now().secondsSinceEpoch().milliseconds());
 }

 extern WTF_EXPORT_PRIVATE const ASCIILiteral weekdayName[7];
 extern WTF_EXPORT_PRIVATE const ASCIILiteral monthName[12];
 extern WTF_EXPORT_PRIVATE const ASCIILiteral monthFullName[12];
 extern WTF_EXPORT_PRIVATE const int firstDayOfMonth[2][12];

 static constexpr double hoursPerDay = 24.0;
 static constexpr double minutesPerHour = 60.0;
 static constexpr double secondsPerMinute = 60.0;
 static constexpr double msPerSecond = 1000.0;
 static constexpr double msPerMonth = 2592000000.0;
 static constexpr double secondsPerHour = secondsPerMinute * minutesPerHour;
 static constexpr double secondsPerDay = secondsPerHour * hoursPerDay;
 static constexpr double msPerMinute = msPerSecond * secondsPerMinute;
 static constexpr double msPerHour = msPerSecond * secondsPerHour;
 static constexpr double msPerDay = msPerSecond * secondsPerDay;

 static constexpr double maxUnixTime = 2145859200.0; // 12/31/2037
 // ECMAScript asks not to support for a date of which total
 // millisecond value is larger than the following value.
 // See 15.9.1.14 of ECMA-262 5th edition.
 static constexpr double maxECMAScriptTime = 8.64E15;

 class TimeClippedPositiveMilliseconds {
 public:
     static constexpr int64_t hoursPerDay = 24;
     static constexpr int64_t minutesPerHour = 60;
     static constexpr int64_t secondsPerMinute = 60;
     static constexpr int64_t msPerSecond = 1000;
     static constexpr int64_t msPerMonth = 2592000000;
     static constexpr int64_t secondsPerHour = secondsPerMinute * minutesPerHour;
     static constexpr int64_t secondsPerDay = secondsPerHour * hoursPerDay;
     static constexpr int64_t msPerMinute = msPerSecond * secondsPerMinute;
     static constexpr int64_t msPerHour = msPerSecond * secondsPerHour;
     static constexpr int64_t msPerDay = msPerSecond * secondsPerDay;
     static constexpr int64_t maxECMAScriptTime = 8.64E15;

     explicit TimeClippedPositiveMilliseconds(int64_t value)
         : m_value(value)
     {
         ASSERT(value >= 0);
     }

     int64_t value() const { return m_value; }
     double asDouble() const { return static_cast<double>(m_value); }
 private:
     int64_t m_value;
 };

 inline double timeClip(double t)
 {
     if (std::abs(t) > maxECMAScriptTime)
         return std::numeric_limits<double>::quiet_NaN();
     return std::trunc(t) + 0.0;
 }

 inline double daysFrom1970ToYear(int year)
 {
     // The Gregorian Calendar rules for leap years:
     // Every fourth year is a leap year. 2004, 2008, and 2012 are leap years.
     // However, every hundredth year is not a leap year. 1900 and 2100 are not leap years.
     // Every four hundred years, there's a leap year after all. 2000 and 2400 are leap years.

     static constexpr int leapDaysBefore1971By4Rule = 1970 / 4;
     static constexpr int excludedLeapDaysBefore1971By100Rule = 1970 / 100;
     static constexpr int leapDaysBefore1971By400Rule = 1970 / 400;

     const double yearMinusOne = static_cast<double>(year) - 1;
     const double yearsToAddBy4Rule = floor(yearMinusOne / 4.0) - leapDaysBefore1971By4Rule;
     const double yearsToExcludeBy100Rule = floor(yearMinusOne / 100.0) - excludedLeapDaysBefore1971By100Rule;
     const double yearsToAddBy400Rule = floor(yearMinusOne / 400.0) - leapDaysBefore1971By400Rule;

     return 365.0 * (year - 1970.0) + yearsToAddBy4Rule - yearsToExcludeBy100Rule + yearsToAddBy400Rule;
 }

 inline int64_t daysFrom1970ToYearTimeClippedPositive(int year)
 {
     static constexpr int leapDaysBefore1971By4Rule = 1970 / 4;
     static constexpr int excludedLeapDaysBefore1971By100Rule = 1970 / 100;
     static constexpr int leapDaysBefore1971By400Rule = 1970 / 400;

     ASSERT(year >= 1970);
     const int64_t yearMinusOne = year - 1;
     const int64_t yearsToAddBy4Rule = yearMinusOne / 4.0 - leapDaysBefore1971By4Rule;
     const int64_t yearsToExcludeBy100Rule = yearMinusOne / 100.0 - excludedLeapDaysBefore1971By100Rule;
     const int64_t yearsToAddBy400Rule = yearMinusOne / 400.0 - leapDaysBefore1971By400Rule;

     return 365 * (year - 1970) + yearsToAddBy4Rule - yearsToExcludeBy100Rule + yearsToAddBy400Rule;
 }

 inline bool isLeapYear(int year)
 {
     if (year % 4 != 0)
         return false;
     if (year % 400 == 0)
         return true;
     if (year % 100 == 0)
         return false;
     return true;
 }

 inline int daysInYear(int year)
 {
     return 365 + isLeapYear(year);
 }

 inline double msToDays(double ms)
 {
     return floor(ms / msPerDay);
 }

 inline int64_t msToDays(TimeClippedPositiveMilliseconds ms)
 {
     return ms.value() / TimeClippedPositiveMilliseconds::msPerDay;
 }

 inline int dayInYear(int year, int month, int day)
 {
     return firstDayOfMonth[isLeapYear(year)][month] + day - 1;
 }

 inline int dayInYear(double ms, int year)
 {
     double result = msToDays(ms) - daysFrom1970ToYear(year);
     return std::isnan(result) ? 0 : static_cast<int>(result);
 }

 inline int dayInYear(TimeClippedPositiveMilliseconds ms, int year)
 {
     return static_cast<int>(msToDays(ms) - daysFrom1970ToYearTimeClippedPositive(year));
 }

 // Returns the number of days from 1970-01-01 to the specified date.
 inline double dateToDaysFrom1970(int year, int month, int day)
 {
     year += month / 12;

     month %= 12;
     if (month < 0) {
         month += 12;
         --year;
     }

     double yearday = floor(daysFrom1970ToYear(year));
     ASSERT((year >= 1970 && yearday >= 0) || (year < 1970 && yearday < 0));
     return yearday + dayInYear(year, month, day);
 }

 inline int msToYear(double ms)
 {
     double msAsYears = std::floor(ms / (msPerDay * 365.2425));
     if (std::isnan(msAsYears))
         msAsYears = 0;
     int approxYear = static_cast<int>(msAsYears + 1970);
     double msFromApproxYearTo1970 = msPerDay * daysFrom1970ToYear(approxYear);
     if (msFromApproxYearTo1970 > ms)
         return approxYear - 1;
     if (msFromApproxYearTo1970 + msPerDay * daysInYear(approxYear) <= ms)
         return approxYear + 1;
     return approxYear;
 }

 inline int msToMinutes(double ms)
 {
     double result = fmod(floor(ms / msPerMinute), minutesPerHour);
     if (result < 0)
         result += minutesPerHour;
     return static_cast<int>(result);
 }

 inline int msToMinutes(TimeClippedPositiveMilliseconds ms)
 {
     int64_t result = (ms.value() / TimeClippedPositiveMilliseconds::msPerMinute) % TimeClippedPositiveMilliseconds::minutesPerHour;
     ASSERT(result >= 0);
     return static_cast<int>(result);
 }

 inline int msToHours(double ms)
 {
     double result = fmod(floor(ms / msPerHour), hoursPerDay);
     if (result < 0)
         result += hoursPerDay;
     return static_cast<int>(result);
 }

 inline int msToHours(TimeClippedPositiveMilliseconds ms)
 {
     int64_t result = (ms.value() / TimeClippedPositiveMilliseconds::msPerHour) % TimeClippedPositiveMilliseconds::hoursPerDay;
     ASSERT(result >= 0);
     return static_cast<int>(result);
 }

 inline int msToSeconds(double ms)
 {
     double result = fmod(floor(ms / msPerSecond), secondsPerMinute);
     if (result < 0)
         result += secondsPerMinute;
     return static_cast<int>(result);
 }

 inline int msToSeconds(TimeClippedPositiveMilliseconds ms)
 {
     int64_t result = ms.value() / TimeClippedPositiveMilliseconds::msPerSecond % TimeClippedPositiveMilliseconds::secondsPerMinute;
     ASSERT(result >= 0);
     return static_cast<int>(result);
 }

 // 0: Sunday, 1: Monday, etc.
 inline int msToWeekDay(double ms)
 {
     int wd = (static_cast<int>(msToDays(ms)) + 4) % 7;
     if (wd < 0)
         wd += 7;
     return wd;
 }

 inline int msToWeekDay(TimeClippedPositiveMilliseconds ms)
 {
     int result = (static_cast<int>(msToDays(ms)) + 4) % 7;
     ASSERT(result >= 0);
     return result;
 }

 inline int monthFromDayInYear(int dayInYear, bool leapYear)
 {
     const int d = dayInYear;
     int step;

     if (d < (step = 31))
         return 0;
     step += (leapYear ? 29 : 28);
     if (d < step)
         return 1;
     if (d < (step += 31))
         return 2;
     if (d < (step += 30))
         return 3;
     if (d < (step += 31))
         return 4;
     if (d < (step += 30))
         return 5;
     if (d < (step += 31))
         return 6;
     if (d < (step += 31))
         return 7;
     if (d < (step += 30))
         return 8;
     if (d < (step += 31))
         return 9;
     if (d < step + 30)
         return 10;
     return 11;
 }

 inline int dayInMonthFromDayInYear(int dayInYear, bool leapYear)
 {
     auto checkMonth = [] (int dayInYear, int& startDayOfThisMonth, int& startDayOfNextMonth, int daysInThisMonth) -> bool {
         startDayOfThisMonth = startDayOfNextMonth;
         startDayOfNextMonth += daysInThisMonth;
         return (dayInYear <= startDayOfNextMonth);
     };

     const int d = dayInYear;
     int step;
     int next = 30;

     if (d <= next)
         return d + 1;
     const int daysInFeb = (leapYear ? 29 : 28);
     if (checkMonth(d, step, next, daysInFeb))
         return d - step;
     if (checkMonth(d, step, next, 31))
         return d - step;
     if (checkMonth(d, step, next, 30))
         return d - step;
     if (checkMonth(d, step, next, 31))
         return d - step;
     if (checkMonth(d, step, next, 30))
         return d - step;
     if (checkMonth(d, step, next, 31))
         return d - step;
     if (checkMonth(d, step, next, 31))
         return d - step;
     if (checkMonth(d, step, next, 30))
         return d - step;
     if (checkMonth(d, step, next, 31))
         return d - step;
     if (checkMonth(d, step, next, 30))
         return d - step;
     step = next;
     return d - step;
 }

 inline double timeToMS(double hour, double min, double sec, double ms)
 {
     return (((hour * WTF::minutesPerHour + min) * WTF::secondsPerMinute + sec) * WTF::msPerSecond + ms);
 }

 WTF_EXPORT_PRIVATE bool isTimeZoneValid(StringView);
 WTF_EXPORT_PRIVATE bool setTimeZoneOverride(StringView);
 WTF_EXPORT_PRIVATE void getTimeZoneOverride(Vector<UChar, 32>& timeZoneID);

 // Returns combined offset in millisecond (UTC + DST).
 WTF_EXPORT_PRIVATE LocalTimeOffset calculateLocalTimeOffset(double utcInMilliseconds, TimeType = UTCTime);

 } // namespace WTF

 using WTF::calculateLocalTimeOffset;
 using WTF::dateToDaysFrom1970;
 using WTF::dayInMonthFromDayInYear;
 using WTF::dayInYear;
 using WTF::getTimeZoneOverride;
 using WTF::isLeapYear;
 using WTF::isTimeZoneValid;
 using WTF::jsCurrentTime;
 using WTF::LocalTimeOffset;
 using WTF::makeRFC2822DateString;
 using WTF::minutesPerHour;
 using WTF::monthFromDayInYear;
 using WTF::msPerDay;
 using WTF::msPerHour;
 using WTF::msPerMinute;
 using WTF::msPerSecond;
 using WTF::msToDays;
 using WTF::msToHours;
 using WTF::msToMinutes;
 using WTF::msToYear;
 using WTF::parseDateFromNullTerminatedCharacters;
 using WTF::secondsPerDay;
 using WTF::secondsPerMinute;
 using WTF::setTimeZoneOverride;
 using WTF::timeClip;
 using WTF::timeToMS;
	/*
	* Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
	* Copyright (C) 2006-2020 Apple Inc. All rights reserved.
	* Copyright (C) 2009 Google Inc. All rights reserved.
	* Copyright (C) 2010 Research In Motion Limited. All rights reserved.
	*
	* Version: MPL 1.1/GPL 2.0/LGPL 2.1
	*
	* The contents of this file are subject to the Mozilla Public License Version
	* 1.1 (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	* http://www.mozilla.org/MPL/
	*
	* Software distributed under the License is distributed on an "AS IS" basis,
	* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
	* for the specific language governing rights and limitations under the
	* License.
	*
	* The Original Code is Mozilla Communicator client code, released
	* March 31, 1998.
	*
	* The Initial Developer of the Original Code is
	* Netscape Communications Corporation.
	* Portions created by the Initial Developer are Copyright (C) 1998
	* the Initial Developer. All Rights Reserved.
	*
	* Contributor(s):
	*
	* Alternatively, the contents of this file may be used under the terms of
	* either of the GNU General Public License Version 2 or later (the "GPL"),
	* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
	* in which case the provisions of the GPL or the LGPL are applicable instead
	* of those above. If you wish to allow use of your version of this file only
	* under the terms of either the GPL or the LGPL, and not to allow others to
	* use your version of this file under the terms of the MPL, indicate your
	* decision by deleting the provisions above and replace them with the notice
	* and other provisions required by the GPL or the LGPL. If you do not delete
	* the provisions above, a recipient may use your version of this file under
	* the terms of any one of the MPL, the GPL or the LGPL.
	*
	*/

	#pragma once

	#include <math.h>
	#include <stdint.h>
	#include <string.h>
	#include <time.h>
	#include <wtf/WallTime.h>
	#include <wtf/text/WTFString.h>

	namespace WTF {

	enum TimeType {
	UTCTime = 0,
	LocalTime
	};

	struct LocalTimeOffset {
	WTF_MAKE_STRUCT_FAST_ALLOCATED;

	LocalTimeOffset() = default;
	constexpr LocalTimeOffset(bool isDST, int offset)
	: isDST(isDST)
	, offset(offset)
	{
	}

	bool operator==(const LocalTimeOffset& other) const
	{
	return isDST == other.isDST && offset == other.offset;
	}

	bool operator!=(const LocalTimeOffset& other) const
	{
	return isDST != other.isDST \|\| offset != other.offset;
	}

	bool isDST { false };
	int offset { 0 };
	};

	void initializeDates();
	int equivalentYearForDST(int year);

	// Not really math related, but this is currently the only shared place to put these.
	WTF_EXPORT_PRIVATE double parseES5DateFromNullTerminatedCharacters(const char* dateString, bool& isLocalTime);
	WTF_EXPORT_PRIVATE double parseDateFromNullTerminatedCharacters(const char* dateString);
	WTF_EXPORT_PRIVATE double parseDateFromNullTerminatedCharacters(const char* dateString, bool& isLocalTime);
	// dayOfWeek: [0, 6] 0 being Monday, day: [1, 31], month: [0, 11], year: ex: 2011, hours: [0, 23], minutes: [0, 59], seconds: [0, 59], utcOffset: [-720,720].
	WTF_EXPORT_PRIVATE String makeRFC2822DateString(unsigned dayOfWeek, unsigned day, unsigned month, unsigned year, unsigned hours, unsigned minutes, unsigned seconds, int utcOffset);

	inline double jsCurrentTime()
	{
	// JavaScript doesn't recognize fractions of a millisecond.
	return floor(WallTime::now().secondsSinceEpoch().milliseconds());
	}

	extern WTF_EXPORT_PRIVATE const ASCIILiteral weekdayName[7];
	extern WTF_EXPORT_PRIVATE const ASCIILiteral monthName[12];
	extern WTF_EXPORT_PRIVATE const ASCIILiteral monthFullName[12];
	extern WTF_EXPORT_PRIVATE const int firstDayOfMonth[2][12];

	static constexpr double hoursPerDay = 24.0;
	static constexpr double minutesPerHour = 60.0;
	static constexpr double secondsPerMinute = 60.0;
	static constexpr double msPerSecond = 1000.0;
	static constexpr double msPerMonth = 2592000000.0;
	static constexpr double secondsPerHour = secondsPerMinute * minutesPerHour;
	static constexpr double secondsPerDay = secondsPerHour * hoursPerDay;
	static constexpr double msPerMinute = msPerSecond * secondsPerMinute;
	static constexpr double msPerHour = msPerSecond * secondsPerHour;
	static constexpr double msPerDay = msPerSecond * secondsPerDay;

	static constexpr double maxUnixTime = 2145859200.0; // 12/31/2037
	// ECMAScript asks not to support for a date of which total
	// millisecond value is larger than the following value.
	// See 15.9.1.14 of ECMA-262 5th edition.
	static constexpr double maxECMAScriptTime = 8.64E15;

	class TimeClippedPositiveMilliseconds {
	public:
	static constexpr int64_t hoursPerDay = 24;
	static constexpr int64_t minutesPerHour = 60;
	static constexpr int64_t secondsPerMinute = 60;
	static constexpr int64_t msPerSecond = 1000;
	static constexpr int64_t msPerMonth = 2592000000;
	static constexpr int64_t secondsPerHour = secondsPerMinute * minutesPerHour;
	static constexpr int64_t secondsPerDay = secondsPerHour * hoursPerDay;
	static constexpr int64_t msPerMinute = msPerSecond * secondsPerMinute;
	static constexpr int64_t msPerHour = msPerSecond * secondsPerHour;
	static constexpr int64_t msPerDay = msPerSecond * secondsPerDay;
	static constexpr int64_t maxECMAScriptTime = 8.64E15;

	explicit TimeClippedPositiveMilliseconds(int64_t value)
	: m_value(value)
	{
	ASSERT(value >= 0);
	}

	int64_t value() const { return m_value; }
	double asDouble() const { return static_cast<double>(m_value); }
	private:
	int64_t m_value;
	};

	inline double timeClip(double t)
	{
	if (std::abs(t) > maxECMAScriptTime)
	return std::numeric_limits<double>::quiet_NaN();
	return std::trunc(t) + 0.0;
	}

	inline double daysFrom1970ToYear(int year)
	{
	// The Gregorian Calendar rules for leap years:
	// Every fourth year is a leap year. 2004, 2008, and 2012 are leap years.
	// However, every hundredth year is not a leap year. 1900 and 2100 are not leap years.
	// Every four hundred years, there's a leap year after all. 2000 and 2400 are leap years.

	static constexpr int leapDaysBefore1971By4Rule = 1970 / 4;
	static constexpr int excludedLeapDaysBefore1971By100Rule = 1970 / 100;
	static constexpr int leapDaysBefore1971By400Rule = 1970 / 400;

	const double yearMinusOne = static_cast<double>(year) - 1;
	const double yearsToAddBy4Rule = floor(yearMinusOne / 4.0) - leapDaysBefore1971By4Rule;
	const double yearsToExcludeBy100Rule = floor(yearMinusOne / 100.0) - excludedLeapDaysBefore1971By100Rule;
	const double yearsToAddBy400Rule = floor(yearMinusOne / 400.0) - leapDaysBefore1971By400Rule;

	return 365.0 * (year - 1970.0) + yearsToAddBy4Rule - yearsToExcludeBy100Rule + yearsToAddBy400Rule;
	}

	inline int64_t daysFrom1970ToYearTimeClippedPositive(int year)
	{
	static constexpr int leapDaysBefore1971By4Rule = 1970 / 4;
	static constexpr int excludedLeapDaysBefore1971By100Rule = 1970 / 100;
	static constexpr int leapDaysBefore1971By400Rule = 1970 / 400;

	ASSERT(year >= 1970);
	const int64_t yearMinusOne = year - 1;
	const int64_t yearsToAddBy4Rule = yearMinusOne / 4.0 - leapDaysBefore1971By4Rule;
	const int64_t yearsToExcludeBy100Rule = yearMinusOne / 100.0 - excludedLeapDaysBefore1971By100Rule;
	const int64_t yearsToAddBy400Rule = yearMinusOne / 400.0 - leapDaysBefore1971By400Rule;

	return 365 * (year - 1970) + yearsToAddBy4Rule - yearsToExcludeBy100Rule + yearsToAddBy400Rule;
	}

	inline bool isLeapYear(int year)
	{
	if (year % 4 != 0)
	return false;
	if (year % 400 == 0)
	return true;
	if (year % 100 == 0)
	return false;
	return true;
	}

	inline int daysInYear(int year)
	{
	return 365 + isLeapYear(year);
	}

	inline double msToDays(double ms)
	{
	return floor(ms / msPerDay);
	}

	inline int64_t msToDays(TimeClippedPositiveMilliseconds ms)
	{
	return ms.value() / TimeClippedPositiveMilliseconds::msPerDay;
	}

	inline int dayInYear(int year, int month, int day)
	{
	return firstDayOfMonth[isLeapYear(year)][month] + day - 1;
	}

	inline int dayInYear(double ms, int year)
	{
	double result = msToDays(ms) - daysFrom1970ToYear(year);
	return std::isnan(result) ? 0 : static_cast<int>(result);
	}

	inline int dayInYear(TimeClippedPositiveMilliseconds ms, int year)
	{
	return static_cast<int>(msToDays(ms) - daysFrom1970ToYearTimeClippedPositive(year));
	}

	// Returns the number of days from 1970-01-01 to the specified date.
	inline double dateToDaysFrom1970(int year, int month, int day)
	{
	year += month / 12;

	month %= 12;
	if (month < 0) {
	month += 12;
	--year;
	}

	double yearday = floor(daysFrom1970ToYear(year));
	ASSERT((year >= 1970 && yearday >= 0) \|\| (year < 1970 && yearday < 0));
	return yearday + dayInYear(year, month, day);
	}

	inline int msToYear(double ms)
	{
	double msAsYears = std::floor(ms / (msPerDay * 365.2425));
	if (std::isnan(msAsYears))
	msAsYears = 0;
	int approxYear = static_cast<int>(msAsYears + 1970);
	double msFromApproxYearTo1970 = msPerDay * daysFrom1970ToYear(approxYear);
	if (msFromApproxYearTo1970 > ms)
	return approxYear - 1;
	if (msFromApproxYearTo1970 + msPerDay * daysInYear(approxYear) <= ms)
	return approxYear + 1;
	return approxYear;
	}

	inline int msToMinutes(double ms)
	{
	double result = fmod(floor(ms / msPerMinute), minutesPerHour);
	if (result < 0)
	result += minutesPerHour;
	return static_cast<int>(result);
	}

	inline int msToMinutes(TimeClippedPositiveMilliseconds ms)
	{
	int64_t result = (ms.value() / TimeClippedPositiveMilliseconds::msPerMinute) % TimeClippedPositiveMilliseconds::minutesPerHour;
	ASSERT(result >= 0);
	return static_cast<int>(result);
	}

	inline int msToHours(double ms)
	{
	double result = fmod(floor(ms / msPerHour), hoursPerDay);
	if (result < 0)
	result += hoursPerDay;
	return static_cast<int>(result);
	}

	inline int msToHours(TimeClippedPositiveMilliseconds ms)
	{
	int64_t result = (ms.value() / TimeClippedPositiveMilliseconds::msPerHour) % TimeClippedPositiveMilliseconds::hoursPerDay;
	ASSERT(result >= 0);
	return static_cast<int>(result);
	}

	inline int msToSeconds(double ms)
	{
	double result = fmod(floor(ms / msPerSecond), secondsPerMinute);
	if (result < 0)
	result += secondsPerMinute;
	return static_cast<int>(result);
	}

	inline int msToSeconds(TimeClippedPositiveMilliseconds ms)
	{
	int64_t result = ms.value() / TimeClippedPositiveMilliseconds::msPerSecond % TimeClippedPositiveMilliseconds::secondsPerMinute;
	ASSERT(result >= 0);
	return static_cast<int>(result);
	}

	// 0: Sunday, 1: Monday, etc.
	inline int msToWeekDay(double ms)
	{
	int wd = (static_cast<int>(msToDays(ms)) + 4) % 7;
	if (wd < 0)
	wd += 7;
	return wd;
	}

	inline int msToWeekDay(TimeClippedPositiveMilliseconds ms)
	{
	int result = (static_cast<int>(msToDays(ms)) + 4) % 7;
	ASSERT(result >= 0);
	return result;
	}

	inline int monthFromDayInYear(int dayInYear, bool leapYear)
	{
	const int d = dayInYear;
	int step;

	if (d < (step = 31))
	return 0;
	step += (leapYear ? 29 : 28);
	if (d < step)
	return 1;
	if (d < (step += 31))
	return 2;
	if (d < (step += 30))
	return 3;
	if (d < (step += 31))
	return 4;
	if (d < (step += 30))
	return 5;
	if (d < (step += 31))
	return 6;
	if (d < (step += 31))
	return 7;
	if (d < (step += 30))
	return 8;
	if (d < (step += 31))
	return 9;
	if (d < step + 30)
	return 10;
	return 11;
	}

	inline int dayInMonthFromDayInYear(int dayInYear, bool leapYear)
	{
	auto checkMonth = [] (int dayInYear, int& startDayOfThisMonth, int& startDayOfNextMonth, int daysInThisMonth) -> bool {
	startDayOfThisMonth = startDayOfNextMonth;
	startDayOfNextMonth += daysInThisMonth;
	return (dayInYear <= startDayOfNextMonth);
	};

	const int d = dayInYear;
	int step;
	int next = 30;

	if (d <= next)
	return d + 1;
	const int daysInFeb = (leapYear ? 29 : 28);
	if (checkMonth(d, step, next, daysInFeb))
	return d - step;
	if (checkMonth(d, step, next, 31))
	return d - step;
	if (checkMonth(d, step, next, 30))
	return d - step;
	if (checkMonth(d, step, next, 31))
	return d - step;
	if (checkMonth(d, step, next, 30))
	return d - step;
	if (checkMonth(d, step, next, 31))
	return d - step;
	if (checkMonth(d, step, next, 31))
	return d - step;
	if (checkMonth(d, step, next, 30))
	return d - step;
	if (checkMonth(d, step, next, 31))
	return d - step;
	if (checkMonth(d, step, next, 30))
	return d - step;
	step = next;
	return d - step;
	}

	inline double timeToMS(double hour, double min, double sec, double ms)
	{
	return (((hour * WTF::minutesPerHour + min) * WTF::secondsPerMinute + sec) * WTF::msPerSecond + ms);
	}

	WTF_EXPORT_PRIVATE bool isTimeZoneValid(StringView);
	WTF_EXPORT_PRIVATE bool setTimeZoneOverride(StringView);
	WTF_EXPORT_PRIVATE void getTimeZoneOverride(Vector<UChar, 32>& timeZoneID);

	// Returns combined offset in millisecond (UTC + DST).
	WTF_EXPORT_PRIVATE LocalTimeOffset calculateLocalTimeOffset(double utcInMilliseconds, TimeType = UTCTime);

	} // namespace WTF

	using WTF::calculateLocalTimeOffset;
	using WTF::dateToDaysFrom1970;
	using WTF::dayInMonthFromDayInYear;
	using WTF::dayInYear;
	using WTF::getTimeZoneOverride;
	using WTF::isLeapYear;
	using WTF::isTimeZoneValid;
	using WTF::jsCurrentTime;
	using WTF::LocalTimeOffset;
	using WTF::makeRFC2822DateString;
	using WTF::minutesPerHour;
	using WTF::monthFromDayInYear;
	using WTF::msPerDay;
	using WTF::msPerHour;
	using WTF::msPerMinute;
	using WTF::msPerSecond;
	using WTF::msToDays;
	using WTF::msToHours;
	using WTF::msToMinutes;
	using WTF::msToYear;
	using WTF::parseDateFromNullTerminatedCharacters;
	using WTF::secondsPerDay;
	using WTF::secondsPerMinute;
	using WTF::setTimeZoneOverride;
	using WTF::timeClip;
	using WTF::timeToMS;