datemath.cpp

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        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;
}

void initDateMath()
{
#ifndef NDEBUG
    static bool alreadyInitialized;
    ASSERT(!alreadyInitialized++);
#endif

    equivalentYearForDST(2000); // Need to call once to initialize a static used in this function.
#if PLATFORM(DARWIN)
    // Register for a notification whenever the time zone changes.
    uint32_t status = notify_register_check("com.apple.system.timezone", &s_notificationToken);
    if (status == NOTIFY_STATUS_OK) {
        s_cachedUTCOffset = calculateUTCOffset();
        s_haveCachedUTCOffset = true;
    }
#endif
}

static inline double ymdhmsToSeconds(long year, int mon, int day, int hour, int minute, int 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 !PLATFORM(WIN_OS)
    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 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 == LONG_MIN || *result == LONG_MAX)
        return false;
    return true;
}

double parseDate(const UString &date)
{
    // 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.

    CString dateCString = date.UTF8String();
    const char *dateString = dateCString.c_str();
     
    // 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 NaN;

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

    if (!*dateString)
        return NaN;

    if (day < 0)
        return NaN;

    long year = 0;
    if (day > 31) {
        // ### where is the boundary and what happens below?
        if (*dateString != '/')
            return NaN;
        // looks like a YYYY/MM/DD date
        if (!*++dateString)
            return NaN;
        year = day;
        if (!parseLong(dateString, &newPosStr, 10, &month))
            return NaN;
        month -= 1;
        dateString = newPosStr;
        if (*dateString++ != '/' || !*dateString)
            return NaN;
        if (!parseLong(dateString, &newPosStr, 10, &day))
            return 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 NaN;
        if (day < 1 || day > 31)
            return NaN;
        dateString = newPosStr;
        if (*dateString == '/')
            dateString++;
        if (!*dateString)
            return NaN;
     } else {
        if (*dateString == '-')
            dateString++;

        skipSpacesAndComments(dateString);

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

        if (month == -1) { // not found yet
            month = findMonth(dateString);
            if (month == -1)
                return NaN;

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

            if (!*dateString)
                return NaN;

            // '-99 23:12:40 GMT'
            if (*dateString != '-' && *dateString != '/' && *dateString != ',' && !isASCIISpace(*dateString))
                return NaN;
            dateString++;
        }
    }

    if (month < 0 || month > 11)
        return NaN;

    // '99 23:12:40 GMT'
    if (year <= 0 && *dateString) {
        if (!parseLong(dateString, &newPosStr, 10, &year))
            return 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 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 NaN;

            if (!*dateString)
                return NaN;

            // ':12:40 GMT'
            if (*dateString++ != ':')
                return NaN;

            if (!parseLong(dateString, &newPosStr, 10, &minute))
                return NaN;
            dateString = newPosStr;

            if (minute < 0 || minute > 59)
                return NaN;

            // ':40 GMT'
            if (*dateString && *dateString != ':' && !isASCIISpace(*dateString))
                return NaN;

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

                if (!parseLong(dateString, &newPosStr, 10, &second))
                    return NaN;
                dateString = newPosStr;
            
                if (second < 0 || second > 59)
                    return NaN;
            }

            skipSpacesAndComments(dateString);

            if (strncasecmp(dateString, "AM", 2) == 0) {
                if (hour > 12)
                    return NaN;
                if (hour == 12)
                    hour = 0;
                dateString += 2;
                skipSpacesAndComments(dateString);
            } else if (strncasecmp(dateString, "PM", 2) == 0) {
                if (hour > 12)
                    return NaN;
                if (hour != 12)
                    hour += 12;
                dateString += 2;
                skipSpacesAndComments(dateString);
            }
        }
    }

    bool haveTZ = false;
    int offset = 0;

    // 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 == '-') {
            long o;
            if (!parseLong(dateString, &newPosStr, 10, &o))
                return NaN;
            dateString = newPosStr;

            if (o < -9959 || o > 9959)
                return NaN;

            int sgn = (o < 0) ? -1 : 1;
            o = abs(o);
            if (*dateString != ':') {
                offset = ((o / 100) * 60 + (o % 100)) * sgn;
            } else { // GMT+05:00
                long o2;
                if (!parseLong(dateString, &newPosStr, 10, &o2))
                    return NaN;
                dateString = newPosStr;
                offset = (o * 60 + o2) * sgn;
            }
            haveTZ = true;
        } else {
            for (int i = 0; i < int(sizeof(known_zones) / sizeof(KnownZone)); 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 (!parseLong(dateString, &newPosStr, 10, &year))
            return NaN;
        dateString = newPosStr;
    }
     
    skipSpacesAndComments(dateString);
     
    // Trailing garbage
    if (*dateString)
        return NaN;

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

    // fall back to local timezone
    if (!haveTZ) {
        GregorianDateTime t;
        t.monthDay = day;
        t.month = month;
        t.year = year - 1900;
        t.isDST = -1;
        t.second = second;
        t.minute = minute;
        t.hour = hour;

        // Use our gregorianDateTimeToMS() rather than mktime() as the latter can't handle the full year range.
        return gregorianDateTimeToMS(t, 0, false);
    }

    return (ymdhmsToSeconds(year, month + 1, day, hour, minute, second) - (offset * 60.0)) * msPerSecond;
}

double timeClip(double t)
{
    if (!isfinite(t))
        return NaN;
    if (fabs(t) > 8.64E15)
        return NaN;
    return trunc(t);
}

UString formatDate(const GregorianDateTime &t)
{
    char buffer[100];
    snprintf(buffer, sizeof(buffer), "%s %s %02d %04d",
        weekdayName[(t.weekDay + 6) % 7],
        monthName[t.month], t.monthDay, t.year + 1900);
    return buffer;
}

UString formatDateUTCVariant(const GregorianDateTime &t)
{
    char buffer[100];
    snprintf(buffer, sizeof(buffer), "%s, %02d %s %04d",
        weekdayName[(t.weekDay + 6) % 7],
        t.monthDay, monthName[t.month], t.year + 1900);
    return buffer;
}

UString formatTime(const GregorianDateTime &t, bool utc)
{
    char buffer[100];
    if (utc) {
        snprintf(buffer, sizeof(buffer), "%02d:%02d:%02d GMT", t.hour, t.minute, t.second);
    } else {
        int offset = abs(gmtoffset(t));
        char tzname[70];
        struct tm gtm = t;
        strftime(tzname, sizeof(tzname), "%Z", &gtm);

        if (tzname[0]) {
            snprintf(buffer, sizeof(buffer), "%02d:%02d:%02d GMT%c%02d%02d (%s)",
                t.hour, t.minute, t.second,
                gmtoffset(t) < 0 ? '-' : '+', offset / (60*60), (offset / 60) % 60, tzname);
        } else {
            snprintf(buffer, sizeof(buffer), "%02d:%02d:%02d GMT%c%02d%02d",
                t.hour, t.minute, t.second,
                gmtoffset(t) < 0 ? '-' : '+', offset / (60*60), (offset / 60) % 60);
        }
    }
    return UString(buffer);
}

} // namespace JSC