Function timeconvert

plugins/mbio/io/MbReader.cpp:173–220

This is an attempt to convert mb_system's poorly defined time_i to adjusted GPS standard time (GPS standard time offset by 1.0E9) Most of this is from converting struct tm (assuming UTC) to time_t from Eric Raymond.

// Most of this is from converting struct tm (assuming UTC) to time_t
// from Eric Raymond.
double timeconvert(int time_i[7])
{
    const uint8_t yearIdx = 0;
    const uint8_t monthIdx = 1;
    const uint8_t dayIdx = 2;
    const uint8_t hourIdx = 3;
    const uint8_t minuteIdx = 4;
    const uint8_t secondIdx = 5;
    const uint8_t microsecIdx = 6;
    const uint8_t monthsPerYear = 12;
    const int cumdays[monthsPerYear] =
        { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };

    long year;
    time_t result;

    year = 1900 + time_i[yearIdx] + time_i[monthIdx] / monthsPerYear;
    result = (year - 1970) * 365 + cumdays[time_i[monthIdx] % monthsPerYear];
    result += (year - 1968) / 4;
    result -= (year - 1900) / 100;
    result += (year - 1600) / 400;
    if ((year % 4) == 0 && ((year % 100) != 0 || (year % 400) == 0) &&
        (time_i[monthIdx] % monthsPerYear) < 2)
        result--;
    result += time_i[dayIdx] - 1;
    result *= 24;
    result += time_i[hourIdx];
    result *= 60;
    result += time_i[minuteIdx];
    result *= 60;
    result += time_i[secondIdx];
    /**
    if (t->tm_isdst == 1)
        result -= 3600;
    **/
    // We should now have time_t in result.  Adjust offset to GPS standard
    // 1/1/1970 to 6/1/1980 in seconds.  Perhaps cleaner than messing with
    // the calculations above which are known to work.
    result -= 315964800;
    // Now subtract seconds for each leap second that has happened between
    // the GPS time root.  These are "announced", so we can't really plan here.
    result -= leapSeconds(time_i[yearIdx], (time_i[monthIdx] / 12) + 1);
    // Now subtract for "adjusted" GPS standard time.
    result -= 1000000000UL;
    // Add back the microseconds as a fraction of a second and convert
    // to double.
    return result + (time_i[microsecIdx] / 1000000.0);
}

} // namespace