JavaScriptCore/kjs/DateMath.cpp

/*
 * Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
 * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
 *
 * 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.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Alternatively, the contents of this file may be used under the terms
 * of either the Mozilla Public License Version 1.1, found at
 * http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
 * License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
 * (the "GPL"), in which case the provisions of the MPL or the GPL are
 * applicable instead of those above.  If you wish to allow use of your
 * version of this file only under the terms of one of those two
 * licenses (the MPL or the GPL) and not to allow others to use your
 * version of this file under the LGPL, indicate your decision by
 * deletingthe provisions above and replace them with the notice and
 * other provisions required by the MPL or the GPL, as the case may be.
 * If you do not delete the provisions above, a recipient may use your
 * version of this file under any of the LGPL, the MPL or the GPL.
 */

#include "config.h"
#include "DateMath.h"

#include <math.h>
#include <stdint.h>
#include <value.h>

#include <wtf/Assertions.h>

#if PLATFORM(DARWIN)
#include <notify.h>
#endif

#if HAVE(SYS_TIME_H)
#include <sys/time.h>
#endif

#if HAVE(SYS_TIMEB_H)
#include <sys/timeb.h>
#endif

#if PLATFORM(WIN_OS)
#include <windows.h>
#endif

namespace KJS {

/* Constants */

static const double minutesPerDay = 24.0 * 60.0;
static const double secondsPerDay = 24.0 * 60.0 * 60.0;
static const double secondsPerYear = 24.0 * 60.0 * 60.0 * 365.0;

static const double usecPerSec = 1000000.0;

static const double maxUnixTime = 2145859200.0; // 12/31/2037

// Day of year for the first day of each month, where index 0 is January, and day 0 is January 1.
// First for non-leap years, then for leap years.
static const int firstDayOfMonth[2][12] = {
    {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
    {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335}
};

static 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;
}

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

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

    const double yearMinusOne = 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) + yearsToAddBy4Rule - yearsToExcludeBy100Rule + yearsToAddBy400Rule;
}

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

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

static inline int dayInYear(double ms, int year)
{
    return static_cast<int>(msToDays(ms) - daysFrom1970ToYear(year));
}

static inline double msToMilliseconds(double ms)
{
    double result = fmod(ms, msPerDay);
    if (result < 0)
        result += msPerDay;
    return result;
}

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

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

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

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

static 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;
}

static inline bool checkMonth(int dayInYear, int& startDayOfThisMonth, int& startDayOfNextMonth, int daysInThisMonth)
{
    startDayOfThisMonth = startDayOfNextMonth;
    startDayOfNextMonth += daysInThisMonth;
    return (dayInYear <= startDayOfNextMonth);
}

static inline int dayInMonthFromDayInYear(int dayInYear, bool leapYear)
{
    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;
}

static inline int monthToDayInYear(int month, bool isLeapYear)
{
    return firstDayOfMonth[isLeapYear][month];
}

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

static int dateToDayInYear(int year, int month, int day)
{
    year += month / 12;

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

    int yearday = static_cast<int>(floor(daysFrom1970ToYear(year)));
    int monthday = monthToDayInYear(month, isLeapYear(year));

    return yearday + monthday + day - 1;
}

#if PLATFORM(WIN_OS)

static LARGE_INTEGER qpcFrequency;
static bool syncedTime;

static double highResUpTime()
{
    // We use QPC, but only after sanity checking its result, due to bugs:
    // http://support.microsoft.com/kb/274323
    // http://support.microsoft.com/kb/895980
    // http://msdn.microsoft.com/en-us/library/ms644904.aspx ("...you can get different results on different processors due to bugs in the basic input/output system (BIOS) or the hardware abstraction layer (HAL)."

    static LARGE_INTEGER qpcLast;
    static DWORD tickCountLast;
    static bool inited;

    LARGE_INTEGER qpc;
    QueryPerformanceCounter(&qpc);
    DWORD tickCount = GetTickCount();

    if (inited) {
        __int64 qpcElapsed = ((qpc.QuadPart - qpcLast.QuadPart) * 1000) / qpcFrequency.QuadPart;
        __int64 tickCountElapsed;
        if (tickCount >= tickCountLast)
            tickCountElapsed = (tickCount - tickCountLast);
        else {
            __int64 tickCountLarge = tickCount + 0x100000000I64;
            tickCountElapsed = tickCountLarge - tickCountLast;
        }

        // force a re-sync if QueryPerformanceCounter differs from GetTickCount by more than 500ms.
        // (500ms value is from http://support.microsoft.com/kb/274323)
        __int64 diff = tickCountElapsed - qpcElapsed;
        if (diff > 500 || diff < -500)
            syncedTime = false;
    } else
        inited = true;

    qpcLast = qpc;
    tickCountLast = tickCount;

    return (1000.0 * qpc.QuadPart) / static_cast<double>(qpcFrequency.QuadPart);;
}

static double lowResUTCTime()
{
    struct _timeb timebuffer;
    _ftime(&timebuffer);
    return timebuffer.time * msPerSecond + timebuffer.millitm;
}

static bool qpcAvailable()
{
    static bool available;
    static bool checked;

    if (checked)
        return available;

    available = QueryPerformanceFrequency(&qpcFrequency);
    checked = true;
    return available;
}

#endif

double getCurrentUTCTime()
{
#if PLATFORM(WIN_OS)
    // Use a combination of ftime and QueryPerformanceCounter.
    // ftime returns the information we want, but doesn't have sufficient resolution.
    // QueryPerformanceCounter has high resolution, but is only usable to measure time intervals.
    // To combine them, we call ftime and QueryPerformanceCounter initially. Later calls will use QueryPerformanceCounter
    // by itself, adding the delta to the saved ftime.  We periodically re-sync to correct for drift.
    static bool started;
    static double syncLowResUTCTime;
    static double syncHighResUpTime;
    static double lastUTCTime;

    double lowResTime = lowResUTCTime();

    if (!qpcAvailable())
        return lowResTime;

    double highResTime = highResUpTime();

    if (!syncedTime) {
        timeBeginPeriod(1); // increase time resolution around low-res time getter
        syncLowResUTCTime = lowResTime = lowResUTCTime();
        timeEndPeriod(1); // restore time resolution
        syncHighResUpTime = highResTime;
        syncedTime = true;
    }

    double highResElapsed = highResTime - syncHighResUpTime;
    double utc = syncLowResUTCTime + highResElapsed;

    // force a clock re-sync if we've drifted
    double lowResElapsed = lowResTime - syncLowResUTCTime;
    const double maximumAllowedDriftMsec = 15.625 * 2.0; // 2x the typical low-res accuracy
    if (fabs(highResElapsed - lowResElapsed) > maximumAllowedDriftMsec)
        syncedTime = false;

    // make sure time doesn't run backwards (only correct if difference is < 2 seconds, since DST or clock changes could occur)
    const double backwardTimeLimit = 2000.0;
    if (utc < lastUTCTime && (lastUTCTime - utc) < backwardTimeLimit)
        return lastUTCTime;
    lastUTCTime = utc;
#else
    struct timeval tv;
    gettimeofday(&tv, 0);
    double utc = floor(tv.tv_sec * msPerSecond + tv.tv_usec / 1000);
#endif
    return utc;
}

// There is a hard limit at 2038 that we currently do not have a workaround
// for (rdar://problem/5052975).
static inline int maximumYearForDST()
{
    return 2037;
}

// It is ok if the cached year is not the current year (e.g. Dec 31st)
// so long as the rules for DST did not change between the two years, if it does
// the app would need to be restarted.
static int mimimumYearForDST()
{
    // Because of the 2038 issue (see maximumYearForDST) if the current year is
    // greater than the max year minus 27 (2010), we want to use the max year
    // minus 27 instead, to ensure there is a range of 28 years that all years
    // can map to.
    static int minYear = std::min(msToYear(getCurrentUTCTime()), maximumYearForDST() - 27) ;
    return minYear;
}

/*
 * Find an equivalent year for the one given, where equivalence is deterined by
 * the two years having the same leapness and the first day of the year, falling
 * on the same day of the week.
 *
 * This function returns a year between this current year and 2037, however this
 * function will potentially return incorrect results if the current year is after
 * 2010, (rdar://problem/5052975), if the year passed in is before 1900 or after
 * 2100, (rdar://problem/5055038).
 */
int equivalentYearForDST(int year)
{
    static int minYear = mimimumYearForDST();
    static int maxYear = maximumYearForDST();
    
    int difference;
    if (year > maxYear)
        difference = minYear - year;
    else if (year < minYear)
        difference = maxYear - year;
    else
        return year;

    int quotient = difference / 28;
    int product = (quotient) * 28;

    year += product;
    ASSERT((year >= minYear && year <= maxYear) || (product - year == static_cast<int>(NaN)));
    return year;
}

/*
 * Get the difference in milliseconds between this time zone and UTC (GMT)
 * NOT including DST.
 */
double getUTCOffset()
{
#if PLATFORM(DARWIN)
    // Register for a notification whenever the time zone changes.
    static bool triedToRegister = false;
    static bool haveNotificationToken = false;
    static int notificationToken;
    if (!triedToRegister) {
        triedToRegister = true;
        uint32_t status = notify_register_check("com.apple.system.timezone", &notificationToken);
        if (status == NOTIFY_STATUS_OK)
            haveNotificationToken = true;
    }

    // If we can verify that we have not received a time zone notification,
    // then use the cached offset from the last time this function was called.
    static bool haveCachedOffset = false;
    static double cachedOffset;
    if (haveNotificationToken && haveCachedOffset) {
        int notified;
        uint32_t status = notify_check(notificationToken, &notified);
        if (status == NOTIFY_STATUS_OK && !notified)
            return cachedOffset;
    }
#endif

    tm localt;

    memset(&localt, 0, sizeof(localt));

    // get the difference between this time zone and UTC on Jan 01, 2000 12:00:00 AM
    localt.tm_mday = 1;
    localt.tm_year = 100;
    double utcOffset = 946684800.0 - mktime(&localt);

    utcOffset *= msPerSecond;

#if PLATFORM(DARWIN)
    haveCachedOffset = true;
    cachedOffset = utcOffset;
#endif

    return utcOffset;
}

/*
 * Get the DST offset for the time passed in.  Takes
 * seconds (not milliseconds) and cannot handle dates before 1970
 * on some OS'
 */
static double getDSTOffsetSimple(double localTimeSeconds, double utcOffset)
{
    if (localTimeSeconds > maxUnixTime)
        localTimeSeconds = maxUnixTime;
    else if (localTimeSeconds < 0) // Go ahead a day to make localtime work (does not work with 0)
        localTimeSeconds += secondsPerDay;

    //input is UTC so we have to shift back to local time to determine DST thus the + getUTCOffset()
    double offsetTime = (localTimeSeconds * msPerSecond) + utcOffset;

    // Offset from UTC but doesn't include DST obviously
    int offsetHour =  msToHours(offsetTime);
    int offsetMinute =  msToMinutes(offsetTime);

    // FIXME: time_t has a potential problem in 2038
    time_t localTime = static_cast<time_t>(localTimeSeconds);

    tm localTM;
#if PLATFORM(QT)
    // ### this is not threadsafe but we don't use multiple threads anyway
    // in the Qt build
#if USE(MULTIPLE_THREADS)
#error Mulitple threads are currently not supported in the Qt/mingw build
#endif
    localTM = *localtime(&localTime);
#elif PLATFORM(WIN_OS)
    #if COMPILER(MSVC7)
    localTM = *localtime(&localTime);
    #else
    localtime_s(&localTM, &localTime);
    #endif
#else
    localtime_r(&localTime, &localTM);
#endif

    double diff = ((localTM.tm_hour - offsetHour) * secondsPerHour) + ((localTM.tm_min - offsetMinute) * 60);

    if (diff < 0)
        diff += secondsPerDay;

    return (diff * msPerSecond);
}

// Get the DST offset, given a time in UTC
static double getDSTOffset(double ms, double utcOffset)
{
    // On Mac OS X, the call to localtime (see getDSTOffsetSimple) will return historically accurate
    // DST information (e.g. New Zealand did not have DST from 1946 to 1974) however the JavaScript
    // standard explicitly dictates that historical information should not be considered when
    // determining DST. For this reason we shift away from years that localtime can handle but would
    // return historically accurate information.
    int year = msToYear(ms);
    int equivalentYear = equivalentYearForDST(year);
    if (year != equivalentYear) {
        bool leapYear = isLeapYear(year);
        int dayInYearLocal = dayInYear(ms, year);
        int dayInMonth = dayInMonthFromDayInYear(dayInYearLocal, leapYear);
        int month = monthFromDayInYear(dayInYearLocal, leapYear);
        int day = dateToDayInYear(equivalentYear, month, dayInMonth);
        ms = (day * msPerDay) + msToMilliseconds(ms);
    }

    return getDSTOffsetSimple(ms / msPerSecond, utcOffset);
}

double gregorianDateTimeToMS(const GregorianDateTime& t, double milliSeconds, bool inputIsUTC)
{
    int day = dateToDayInYear(t.year + 1900, t.month, t.monthDay);
    double ms = timeToMS(t.hour, t.minute, t.second, milliSeconds);
    double result = (day * msPerDay) + ms;

    if (!inputIsUTC) { // convert to UTC
        double utcOffset = getUTCOffset();
        result -= utcOffset;
        result -= getDSTOffset(result, utcOffset);
    }

    return result;
}

void msToGregorianDateTime(double ms, bool outputIsUTC, GregorianDateTime& tm)
{
    // input is UTC
    double dstOff = 0.0;
    const double utcOff = getUTCOffset();
    
    if (!outputIsUTC) {  // convert to local time
        dstOff = getDSTOffset(ms, utcOff);
        ms += dstOff + utcOff;
    }

    const int year = msToYear(ms);
    tm.second   =  msToSeconds(ms);
    tm.minute   =  msToMinutes(ms);
    tm.hour     =  msToHours(ms);
    tm.weekDay  =  msToWeekDay(ms);
    tm.yearDay  =  dayInYear(ms, year);
    tm.monthDay =  dayInMonthFromDayInYear(tm.yearDay, isLeapYear(year));
    tm.month    =  monthFromDayInYear(tm.yearDay, isLeapYear(year));
    tm.year     =  year - 1900;
    tm.isDST    =  dstOff != 0.0;

    tm.utcOffset = static_cast<long>((dstOff + utcOff) / msPerSecond);
    tm.timeZone = NULL;
}

} // namespace KJS