root/Source/wtf/DateMath.cpp

DEFINITIONS

1. getLocalTime
2. isLeapYear
3. daysInYear
4. daysFrom1970ToYear
5. msToDays
6. twoDigitStringFromNumber
7. msToYear
8. dayInYear
9. msToMilliseconds
10. msToMinutes
11. msToHours
12. monthFromDayInYear
13. checkMonth
14. dayInMonthFromDayInYear
15. dayInYear
16. dateToDaysFrom1970
17. maximumYearForDST
18. jsCurrentTime
19. minimumYearForDST
20. equivalentYearForDST
21. calculateUTCOffset
22. calculateDSTOffsetSimple
23. calculateDSTOffset
24. initializeDates
25. ymdhmsToSeconds
26. skipSpacesAndComments
27. findMonth
28. parseInt
29. parseLong
30. parseDateFromNullTerminatedCharacters
31. parseDateFromNullTerminatedCharacters
32. makeRFC2822DateString

/*
 * Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
 * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
 * Copyright (C) 2009 Google Inc. All rights reserved.
 * Copyright (C) 2007-2009 Torch Mobile, Inc.
 * Copyright (C) 2010 &yet, LLC. (nate@andyet.net)
 *
 * 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.

 * Copyright 2006-2008 the V8 project authors. All rights reserved.
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 *       copyright notice, this list of conditions and the following
 *       disclaimer in the documentation and/or other materials provided
 *       with the distribution.
 *     * Neither the name of Google Inc. nor the names of its
 *       contributors may be used to endorse or promote products derived
 *       from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

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

#include "Assertions.h"
#include "ASCIICType.h"
#include "CurrentTime.h"
#include "MathExtras.h"
#include "StdLibExtras.h"
#include "StringExtras.h"

#include <algorithm>
#include <limits.h>
#include <limits>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include "wtf/text/StringBuilder.h"

#if OS(WIN)
#include <windows.h>
#endif

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

using namespace WTF;

namespace WTF {

/* Constants */

static const double hoursPerDay = 24.0;
static const double secondsPerDay = 24.0 * 60.0 * 60.0;
static const double secondsPerHour = 60.0 * 60.0;

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 void getLocalTime(const time_t* localTime, struct tm* localTM)
{
#if COMPILER(MSVC)
    localtime_s(localTM, localTime);
#else
    localtime_r(localTime, localTM);
#endif
}

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

static String twoDigitStringFromNumber(int number)
{
    ASSERT(number >= 0 && number < 100);
    if (number > 9)
        return String::number(number);
    return "0" + String::number(number);
}

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;
}

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;
}

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

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

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);
}

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;
}

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

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);
}

// 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;
}

static inline double jsCurrentTime()
{
    // JavaScript doesn't recognize fractions of a millisecond.
    return floor(WTF::currentTimeMS());
}

static inline int minimumYearForDST()
{
    // 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.
    return std::min(msToYear(jsCurrentTime()), maximumYearForDST() - 27) ;
}

/*
 * 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).
 */
static int equivalentYearForDST(int year)
{
    // It is ok if the cached year is not the current year as long as the rules
    // for DST did not change between the two years; if they did the app would need
    // to be restarted.
    static int minYear = minimumYearForDST();
    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>(std::numeric_limits<double>::quiet_NaN())));
    return year;
}

int32_t calculateUTCOffset()
{
#if OS(WIN)
    TIME_ZONE_INFORMATION timeZoneInformation;
    GetTimeZoneInformation(&timeZoneInformation);
    int32_t bias = timeZoneInformation.Bias + timeZoneInformation.StandardBias;
    return -bias * 60 * 1000;
#else
    time_t localTime = time(0);
    tm localt;
    getLocalTime(&localTime, &localt);

    // Get the difference between this time zone and UTC on the 1st of January of this year.
    localt.tm_sec = 0;
    localt.tm_min = 0;
    localt.tm_hour = 0;
    localt.tm_mday = 1;
    localt.tm_mon = 0;
    // Not setting localt.tm_year!
    localt.tm_wday = 0;
    localt.tm_yday = 0;
    localt.tm_isdst = 0;
#if HAVE(TM_GMTOFF)
    localt.tm_gmtoff = 0;
#endif
#if HAVE(TM_ZONE)
    localt.tm_zone = 0;
#endif

#if HAVE(TIMEGM)
    time_t utcOffset = timegm(&localt) - mktime(&localt);
#else
    // Using a canned date of 01/01/2009 on platforms with weaker date-handling foo.
    localt.tm_year = 109;
    time_t utcOffset = 1230768000 - mktime(&localt);
#endif

    return static_cast<int32_t>(utcOffset * 1000);
#endif
}

/*
 * Get the DST offset for the time passed in.
 */
static double calculateDSTOffsetSimple(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;
    getLocalTime(&localTime, &localTM);

    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
double calculateDSTOffset(double ms, double utcOffset)
{
    // On Mac OS X, the call to localtime (see calculateDSTOffsetSimple) 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);
        double day = dateToDaysFrom1970(equivalentYear, month, dayInMonth);
        ms = (day * msPerDay) + msToMilliseconds(ms);
    }

    return calculateDSTOffsetSimple(ms / msPerSecond, utcOffset);
}

void initializeDates()
{
#if ASSERT_ENABLED
    static bool alreadyInitialized;
    ASSERT(!alreadyInitialized);
    alreadyInitialized = true;
#endif

    equivalentYearForDST(2000); // Need to call once to initialize a static used in this function.
}

static inline double ymdhmsToSeconds(int year, long mon, long day, long hour, long minute, double second)
{
    double days = (day - 32075)
        + floor(1461 * (year + 4800.0 + (mon - 14) / 12) / 4)
        + 367 * (mon - 2 - (mon - 14) / 12 * 12) / 12
        - floor(3 * ((year + 4900.0 + (mon - 14) / 12) / 100) / 4)
        - 2440588;
    return ((days * hoursPerDay + hour) * minutesPerHour + minute) * secondsPerMinute + second;
}

// We follow the recommendation of RFC 2822 to consider all
// obsolete time zones not listed here equivalent to "-0000".
static const struct KnownZone {
#if !OS(WIN)
    const
#endif
        char tzName[4];
    int tzOffset;
} known_zones[] = {
    { "UT", 0 },
    { "GMT", 0 },
    { "EST", -300 },
    { "EDT", -240 },
    { "CST", -360 },
    { "CDT", -300 },
    { "MST", -420 },
    { "MDT", -360 },
    { "PST", -480 },
    { "PDT", -420 }
};

inline static void skipSpacesAndComments(const char*& s)
{
    int nesting = 0;
    char ch;
    while ((ch = *s)) {
        if (!isASCIISpace(ch)) {
            if (ch == '(')
                nesting++;
            else if (ch == ')' && nesting > 0)
                nesting--;
            else if (nesting == 0)
                break;
        }
        s++;
    }
}

// returns 0-11 (Jan-Dec); -1 on failure
static int findMonth(const char* monthStr)
{
    ASSERT(monthStr);
    char needle[4];
    for (int i = 0; i < 3; ++i) {
        if (!*monthStr)
            return -1;
        needle[i] = static_cast<char>(toASCIILower(*monthStr++));
    }
    needle[3] = '\0';
    const char *haystack = "janfebmaraprmayjunjulaugsepoctnovdec";
    const char *str = strstr(haystack, needle);
    if (str) {
        int position = static_cast<int>(str - haystack);
        if (position % 3 == 0)
            return position / 3;
    }
    return -1;
}

static bool parseInt(const char* string, char** stopPosition, int base, int* result)
{
    long longResult = strtol(string, stopPosition, base);
    // Avoid the use of errno as it is not available on Windows CE
    if (string == *stopPosition || longResult <= std::numeric_limits<int>::min() || longResult >= std::numeric_limits<int>::max())
        return false;
    *result = static_cast<int>(longResult);
    return true;
}

static bool parseLong(const char* string, char** stopPosition, int base, long* result)
{
    *result = strtol(string, stopPosition, base);
    // Avoid the use of errno as it is not available on Windows CE
    if (string == *stopPosition || *result == std::numeric_limits<long>::min() || *result == std::numeric_limits<long>::max())
        return false;
    return true;
}

// Odd case where 'exec' is allowed to be 0, to accomodate a caller in WebCore.
static double parseDateFromNullTerminatedCharacters(const char* dateString, bool& haveTZ, int& offset)
{
    haveTZ = false;
    offset = 0;

    // This parses a date in the form:
    //     Tuesday, 09-Nov-99 23:12:40 GMT
    // or
    //     Sat, 01-Jan-2000 08:00:00 GMT
    // or
    //     Sat, 01 Jan 2000 08:00:00 GMT
    // or
    //     01 Jan 99 22:00 +0100    (exceptions in rfc822/rfc2822)
    // ### non RFC formats, added for Javascript:
    //     [Wednesday] January 09 1999 23:12:40 GMT
    //     [Wednesday] January 09 23:12:40 GMT 1999
    //
    // We ignore the weekday.

    // Skip leading space
    skipSpacesAndComments(dateString);

    long month = -1;
    const char *wordStart = dateString;
    // Check contents of first words if not number
    while (*dateString && !isASCIIDigit(*dateString)) {
        if (isASCIISpace(*dateString) || *dateString == '(') {
            if (dateString - wordStart >= 3)
                month = findMonth(wordStart);
            skipSpacesAndComments(dateString);
            wordStart = dateString;
        } else
           dateString++;
    }

    // Missing delimiter between month and day (like "January29")?
    if (month == -1 && wordStart != dateString)
        month = findMonth(wordStart);

    skipSpacesAndComments(dateString);

    if (!*dateString)
        return std::numeric_limits<double>::quiet_NaN();

    // ' 09-Nov-99 23:12:40 GMT'
    char* newPosStr;
    long day;
    if (!parseLong(dateString, &newPosStr, 10, &day))
        return std::numeric_limits<double>::quiet_NaN();
    dateString = newPosStr;

    if (!*dateString)
        return std::numeric_limits<double>::quiet_NaN();

    if (day < 0)
        return std::numeric_limits<double>::quiet_NaN();

    int year = 0;
    if (day > 31) {
        // ### where is the boundary and what happens below?
        if (*dateString != '/')
            return std::numeric_limits<double>::quiet_NaN();
        // looks like a YYYY/MM/DD date
        if (!*++dateString)
            return std::numeric_limits<double>::quiet_NaN();
        if (day <= std::numeric_limits<int>::min() || day >= std::numeric_limits<int>::max())
            return std::numeric_limits<double>::quiet_NaN();
        year = static_cast<int>(day);
        if (!parseLong(dateString, &newPosStr, 10, &month))
            return std::numeric_limits<double>::quiet_NaN();
        month -= 1;
        dateString = newPosStr;
        if (*dateString++ != '/' || !*dateString)
            return std::numeric_limits<double>::quiet_NaN();
        if (!parseLong(dateString, &newPosStr, 10, &day))
            return std::numeric_limits<double>::quiet_NaN();
        dateString = newPosStr;
    } else if (*dateString == '/' && month == -1) {
        dateString++;
        // This looks like a MM/DD/YYYY date, not an RFC date.
        month = day - 1; // 0-based
        if (!parseLong(dateString, &newPosStr, 10, &day))
            return std::numeric_limits<double>::quiet_NaN();
        if (day < 1 || day > 31)
            return std::numeric_limits<double>::quiet_NaN();
        dateString = newPosStr;
        if (*dateString == '/')
            dateString++;
        if (!*dateString)
            return std::numeric_limits<double>::quiet_NaN();
     } else {
        if (*dateString == '-')
            dateString++;

        skipSpacesAndComments(dateString);

        if (*dateString == ',')
            dateString++;

        if (month == -1) { // not found yet
            month = findMonth(dateString);
            if (month == -1)
                return std::numeric_limits<double>::quiet_NaN();

            while (*dateString && *dateString != '-' && *dateString != ',' && !isASCIISpace(*dateString))
                dateString++;

            if (!*dateString)
                return std::numeric_limits<double>::quiet_NaN();

            // '-99 23:12:40 GMT'
            if (*dateString != '-' && *dateString != '/' && *dateString != ',' && !isASCIISpace(*dateString))
                return std::numeric_limits<double>::quiet_NaN();
            dateString++;
        }
    }

    if (month < 0 || month > 11)
        return std::numeric_limits<double>::quiet_NaN();

    // '99 23:12:40 GMT'
    if (year <= 0 && *dateString) {
        if (!parseInt(dateString, &newPosStr, 10, &year))
            return std::numeric_limits<double>::quiet_NaN();
    }

    // Don't fail if the time is missing.
    long hour = 0;
    long minute = 0;
    long second = 0;
    if (!*newPosStr)
        dateString = newPosStr;
    else {
        // ' 23:12:40 GMT'
        if (!(isASCIISpace(*newPosStr) || *newPosStr == ',')) {
            if (*newPosStr != ':')
                return std::numeric_limits<double>::quiet_NaN();
            // There was no year; the number was the hour.
            year = -1;
        } else {
            // in the normal case (we parsed the year), advance to the next number
            dateString = ++newPosStr;
            skipSpacesAndComments(dateString);
        }

        parseLong(dateString, &newPosStr, 10, &hour);
        // Do not check for errno here since we want to continue
        // even if errno was set becasue we are still looking
        // for the timezone!

        // Read a number? If not, this might be a timezone name.
        if (newPosStr != dateString) {
            dateString = newPosStr;

            if (hour < 0 || hour > 23)
                return std::numeric_limits<double>::quiet_NaN();

            if (!*dateString)
                return std::numeric_limits<double>::quiet_NaN();

            // ':12:40 GMT'
            if (*dateString++ != ':')
                return std::numeric_limits<double>::quiet_NaN();

            if (!parseLong(dateString, &newPosStr, 10, &minute))
                return std::numeric_limits<double>::quiet_NaN();
            dateString = newPosStr;

            if (minute < 0 || minute > 59)
                return std::numeric_limits<double>::quiet_NaN();

            // ':40 GMT'
            if (*dateString && *dateString != ':' && !isASCIISpace(*dateString))
                return std::numeric_limits<double>::quiet_NaN();

            // seconds are optional in rfc822 + rfc2822
            if (*dateString ==':') {
                dateString++;

                if (!parseLong(dateString, &newPosStr, 10, &second))
                    return std::numeric_limits<double>::quiet_NaN();
                dateString = newPosStr;

                if (second < 0 || second > 59)
                    return std::numeric_limits<double>::quiet_NaN();
            }

            skipSpacesAndComments(dateString);

            if (strncasecmp(dateString, "AM", 2) == 0) {
                if (hour > 12)
                    return std::numeric_limits<double>::quiet_NaN();
                if (hour == 12)
                    hour = 0;
                dateString += 2;
                skipSpacesAndComments(dateString);
            } else if (strncasecmp(dateString, "PM", 2) == 0) {
                if (hour > 12)
                    return std::numeric_limits<double>::quiet_NaN();
                if (hour != 12)
                    hour += 12;
                dateString += 2;
                skipSpacesAndComments(dateString);
            }
        }
    }

    // The year may be after the time but before the time zone.
    if (isASCIIDigit(*dateString) && year == -1) {
        if (!parseInt(dateString, &newPosStr, 10, &year))
            return std::numeric_limits<double>::quiet_NaN();
        dateString = newPosStr;
        skipSpacesAndComments(dateString);
    }

    // Don't fail if the time zone is missing.
    // Some websites omit the time zone (4275206).
    if (*dateString) {
        if (strncasecmp(dateString, "GMT", 3) == 0 || strncasecmp(dateString, "UTC", 3) == 0) {
            dateString += 3;
            haveTZ = true;
        }

        if (*dateString == '+' || *dateString == '-') {
            int o;
            if (!parseInt(dateString, &newPosStr, 10, &o))
                return std::numeric_limits<double>::quiet_NaN();
            dateString = newPosStr;

            if (o < -9959 || o > 9959)
                return std::numeric_limits<double>::quiet_NaN();

            int sgn = (o < 0) ? -1 : 1;
            o = abs(o);
            if (*dateString != ':') {
                if (o >= 24)
                    offset = ((o / 100) * 60 + (o % 100)) * sgn;
                else
                    offset = o * 60 * sgn;
            } else { // GMT+05:00
                ++dateString; // skip the ':'
                int o2;
                if (!parseInt(dateString, &newPosStr, 10, &o2))
                    return std::numeric_limits<double>::quiet_NaN();
                dateString = newPosStr;
                offset = (o * 60 + o2) * sgn;
            }
            haveTZ = true;
        } else {
            for (size_t i = 0; i < WTF_ARRAY_LENGTH(known_zones); ++i) {
                if (0 == strncasecmp(dateString, known_zones[i].tzName, strlen(known_zones[i].tzName))) {
                    offset = known_zones[i].tzOffset;
                    dateString += strlen(known_zones[i].tzName);
                    haveTZ = true;
                    break;
                }
            }
        }
    }

    skipSpacesAndComments(dateString);

    if (*dateString && year == -1) {
        if (!parseInt(dateString, &newPosStr, 10, &year))
            return std::numeric_limits<double>::quiet_NaN();
        dateString = newPosStr;
        skipSpacesAndComments(dateString);
    }

    // Trailing garbage
    if (*dateString)
        return std::numeric_limits<double>::quiet_NaN();

    // Y2K: Handle 2 digit years.
    if (year >= 0 && year < 100) {
        if (year < 50)
            year += 2000;
        else
            year += 1900;
    }

    return ymdhmsToSeconds(year, month + 1, day, hour, minute, second) * msPerSecond;
}

double parseDateFromNullTerminatedCharacters(const char* dateString)
{
    bool haveTZ;
    int offset;
    double ms = parseDateFromNullTerminatedCharacters(dateString, haveTZ, offset);
    if (std::isnan(ms))
        return std::numeric_limits<double>::quiet_NaN();

    // fall back to local timezone
    if (!haveTZ) {
        double utcOffset = calculateUTCOffset();
        double dstOffset = calculateDSTOffset(ms, utcOffset);
        offset = (utcOffset + dstOffset) / msPerMinute;
    }
    return ms - (offset * msPerMinute);
}

// See http://tools.ietf.org/html/rfc2822#section-3.3 for more information.
String makeRFC2822DateString(unsigned dayOfWeek, unsigned day, unsigned month, unsigned year, unsigned hours, unsigned minutes, unsigned seconds, int utcOffset)
{
    StringBuilder stringBuilder;
    stringBuilder.append(weekdayName[dayOfWeek]);
    stringBuilder.appendLiteral(", ");
    stringBuilder.appendNumber(day);
    stringBuilder.append(' ');
    stringBuilder.append(monthName[month]);
    stringBuilder.append(' ');
    stringBuilder.appendNumber(year);
    stringBuilder.append(' ');

    stringBuilder.append(twoDigitStringFromNumber(hours));
    stringBuilder.append(':');
    stringBuilder.append(twoDigitStringFromNumber(minutes));
    stringBuilder.append(':');
    stringBuilder.append(twoDigitStringFromNumber(seconds));
    stringBuilder.append(' ');

    stringBuilder.append(utcOffset > 0 ? '+' : '-');
    int absoluteUTCOffset = abs(utcOffset);
    stringBuilder.append(twoDigitStringFromNumber(absoluteUTCOffset / 60));
    stringBuilder.append(twoDigitStringFromNumber(absoluteUTCOffset % 60));

    return stringBuilder.toString();
}

} // namespace WTF