DateTime.cc

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// -*- lsst-c++ -*-

/*
 * LSST Data Management System
 * Copyright 2008, 2009, 2010 LSST Corporation.
 *
 * This product includes software developed by the
 * LSST Project (http://www.lsst.org/).
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the LSST License Statement and
 * the GNU General Public License along with this program.  If not,
 * see <http://www.lsstcorp.org/LegalNotices/>.
 */

#include <limits>
#include <cmath>
#include <vector>

#include "boost/format.hpp"
#include "boost/regex.hpp"

#include "lsst/daf/base/DateTime.h"
#include "lsst/pex/exceptions.h"

namespace dafBase = lsst::daf::base;
namespace pexEx   = lsst::pex::exceptions;

// Epoch = 1970 JAN  1 00:00:00 = JD 2440587.5 = MJD 40587.0
static double const MJD_TO_JD = 2400000.5;
static double const EPOCH_IN_MJD = 40587.0;
static double const JD2000 = 2451544.50;

static double const NSEC_PER_DAY = 86.4e12;

static long long const LL_NSEC_PER_SEC = 1000000000LL;
// static long long const LL_NSEC_PER_DAY = 86400 * LL_NSEC_PER_SEC;

// Maximum number of days expressible as signed 64-bit nanoseconds.
// 2^64 / 2 / 1e9 / 86400
// NOTE: long long nsecs will wrap:
// -- earliest date representable = sep 21, 1677 00:00:00
// -- latest date representable   = apr 12, 2262 00:00:00
static double const MAX_DAYS = 106751.99;


#ifdef CAL_TO_JD
static double const HOURS_PER_DAY = 24.0;
static double const MIN_PER_DAY   = 1440.0;
static double const SEC_PER_DAY   = 86400.0;
#endif

// Difference between Terrestrial Time and TAI.
static long long const TT_MINUS_TAI_NSECS = 32184000000LL;

/* Leap second table as string.
 *
 * Source: http://maia.usno.navy.mil/ser7/tai-utc.dat
 */
static std::string leapString =
"\
1961 JAN  1 =JD 2437300.5  TAI-UTC=   1.4228180 S + (MJD - 37300.) X 0.001296 S\n\
1961 AUG  1 =JD 2437512.5  TAI-UTC=   1.3728180 S + (MJD - 37300.) X 0.001296 S\n\
1962 JAN  1 =JD 2437665.5  TAI-UTC=   1.8458580 S + (MJD - 37665.) X 0.0011232S\n\
1963 NOV  1 =JD 2438334.5  TAI-UTC=   1.9458580 S + (MJD - 37665.) X 0.0011232S\n\
1964 JAN  1 =JD 2438395.5  TAI-UTC=   3.2401300 S + (MJD - 38761.) X 0.001296 S\n\
1964 APR  1 =JD 2438486.5  TAI-UTC=   3.3401300 S + (MJD - 38761.) X 0.001296 S\n\
1964 SEP  1 =JD 2438639.5  TAI-UTC=   3.4401300 S + (MJD - 38761.) X 0.001296 S\n\
1965 JAN  1 =JD 2438761.5  TAI-UTC=   3.5401300 S + (MJD - 38761.) X 0.001296 S\n\
1965 MAR  1 =JD 2438820.5  TAI-UTC=   3.6401300 S + (MJD - 38761.) X 0.001296 S\n\
1965 JUL  1 =JD 2438942.5  TAI-UTC=   3.7401300 S + (MJD - 38761.) X 0.001296 S\n\
1965 SEP  1 =JD 2439004.5  TAI-UTC=   3.8401300 S + (MJD - 38761.) X 0.001296 S\n\
1966 JAN  1 =JD 2439126.5  TAI-UTC=   4.3131700 S + (MJD - 39126.) X 0.002592 S\n\
1968 FEB  1 =JD 2439887.5  TAI-UTC=   4.2131700 S + (MJD - 39126.) X 0.002592 S\n\
1972 JAN  1 =JD 2441317.5  TAI-UTC=  10.0       S + (MJD - 41317.) X 0.0      S\n\
1972 JUL  1 =JD 2441499.5  TAI-UTC=  11.0       S + (MJD - 41317.) X 0.0      S\n\
1973 JAN  1 =JD 2441683.5  TAI-UTC=  12.0       S + (MJD - 41317.) X 0.0      S\n\
1974 JAN  1 =JD 2442048.5  TAI-UTC=  13.0       S + (MJD - 41317.) X 0.0      S\n\
1975 JAN  1 =JD 2442413.5  TAI-UTC=  14.0       S + (MJD - 41317.) X 0.0      S\n\
1976 JAN  1 =JD 2442778.5  TAI-UTC=  15.0       S + (MJD - 41317.) X 0.0      S\n\
1977 JAN  1 =JD 2443144.5  TAI-UTC=  16.0       S + (MJD - 41317.) X 0.0      S\n\
1978 JAN  1 =JD 2443509.5  TAI-UTC=  17.0       S + (MJD - 41317.) X 0.0      S\n\
1979 JAN  1 =JD 2443874.5  TAI-UTC=  18.0       S + (MJD - 41317.) X 0.0      S\n\
1980 JAN  1 =JD 2444239.5  TAI-UTC=  19.0       S + (MJD - 41317.) X 0.0      S\n\
1981 JUL  1 =JD 2444786.5  TAI-UTC=  20.0       S + (MJD - 41317.) X 0.0      S\n\
1982 JUL  1 =JD 2445151.5  TAI-UTC=  21.0       S + (MJD - 41317.) X 0.0      S\n\
1983 JUL  1 =JD 2445516.5  TAI-UTC=  22.0       S + (MJD - 41317.) X 0.0      S\n\
1985 JUL  1 =JD 2446247.5  TAI-UTC=  23.0       S + (MJD - 41317.) X 0.0      S\n\
1988 JAN  1 =JD 2447161.5  TAI-UTC=  24.0       S + (MJD - 41317.) X 0.0      S\n\
1990 JAN  1 =JD 2447892.5  TAI-UTC=  25.0       S + (MJD - 41317.) X 0.0      S\n\
1991 JAN  1 =JD 2448257.5  TAI-UTC=  26.0       S + (MJD - 41317.) X 0.0      S\n\
1992 JUL  1 =JD 2448804.5  TAI-UTC=  27.0       S + (MJD - 41317.) X 0.0      S\n\
1993 JUL  1 =JD 2449169.5  TAI-UTC=  28.0       S + (MJD - 41317.) X 0.0      S\n\
1994 JUL  1 =JD 2449534.5  TAI-UTC=  29.0       S + (MJD - 41317.) X 0.0      S\n\
1996 JAN  1 =JD 2450083.5  TAI-UTC=  30.0       S + (MJD - 41317.) X 0.0      S\n\
1997 JUL  1 =JD 2450630.5  TAI-UTC=  31.0       S + (MJD - 41317.) X 0.0      S\n\
1999 JAN  1 =JD 2451179.5  TAI-UTC=  32.0       S + (MJD - 41317.) X 0.0      S\n\
2006 JAN  1 =JD 2453736.5  TAI-UTC=  33.0       S + (MJD - 41317.) X 0.0      S\n\
2009 JAN  1 =JD 2454832.5  TAI-UTC=  34.0       S + (MJD - 41317.) X 0.0      S\n\
2012 JUL  1 =JD 2456109.5  TAI-UTC=  35.0       S + (MJD - 41317.) X 0.0      S\n\
2015 JUL  1 =JD 2457204.5  TAI-UTC=  36.0       S + (MJD - 41317.) X 0.0      S\n\
2017 JAN  1 =JD 2457754.5  TAI-UTC=  37.0       S + (MJD - 41317.) X 0.0      S\n\
";

// Anonymous namespace for structures, classes, and formerly file-static
// functions.
namespace {

struct Leap {
    long long whenUtc; 
    long long whenTai; 
    double offset; 
    double mjdRef; 
    double drift; 
};

class LeapTable : public std::vector<Leap> {
public:
    LeapTable(void);
};

LeapTable leapSecTable;

LeapTable::LeapTable(void) {
    dafBase::DateTime::initializeLeapSeconds(leapString);
}

template<typename NsType>
NsType utcToTai(NsType nsecs) {
    size_t i;
    for (i = 0; i < leapSecTable.size(); ++i) {
        if (nsecs < leapSecTable[i].whenUtc) break;
    }
    if (i == 0) {
        throw LSST_EXCEPT(
            lsst::pex::exceptions::DomainError,
            (boost::format(
                    "DateTime value too early for UTC-TAI conversion: %1%"
                    ) % nsecs).str());
    }
    Leap const& l(leapSecTable[i - 1]);
    double mjd = static_cast<double>(nsecs) / NSEC_PER_DAY + EPOCH_IN_MJD;
    double leapSecs = l.offset + (mjd - l.mjdRef) * l.drift;
    NsType leapNSecs = static_cast<NsType>(leapSecs * 1.0e9 + 0.5);
    return nsecs + leapNSecs;
}

template<typename NsType>
NsType taiToUtc(NsType nsecs) {
    size_t i;
    for (i = 0; i < leapSecTable.size(); ++i) {
        if (nsecs < leapSecTable[i].whenTai) break;
    }
    if (i == 0) {
        throw LSST_EXCEPT(
            lsst::pex::exceptions::DomainError,
            (boost::format(
                    "DateTime value too early for TAI-UTC conversion: %1%"
                    ) % nsecs).str());
    }
    Leap const& l(leapSecTable[i - 1]);
    double mjd = static_cast<double>(nsecs) / NSEC_PER_DAY + EPOCH_IN_MJD;
    double leapSecs = l.offset + (mjd - l.mjdRef) * l.drift;
    // Correct for TAI MJD vs. UTC MJD.
    leapSecs /= 1.0 + l.drift * 1.0e9 / NSEC_PER_DAY;
    NsType leapNSecs = static_cast<NsType>(leapSecs * 1.0e9 + 0.5);
    return nsecs - leapNSecs;
}

long long nsecAnyToTai(long long nsecs, dafBase::DateTime::Timescale scale) {
    switch(scale) {
        case dafBase::DateTime::TAI:
            return nsecs;
        case dafBase::DateTime::TT:
            return nsecs - TT_MINUS_TAI_NSECS;
        case dafBase::DateTime::UTC:
            return utcToTai(nsecs);
    }
    std::ostringstream os;
    os << "Unsupported scale " << scale;
    throw LSST_EXCEPT(lsst::pex::exceptions::InvalidParameterError, os.str());
}

long long nsecTaiToAny(long long nsecs, dafBase::DateTime::Timescale scale) {
    switch(scale) {
        case dafBase::DateTime::TAI:
            return nsecs;
        case dafBase::DateTime::TT:
            return nsecs + TT_MINUS_TAI_NSECS;
        case dafBase::DateTime::UTC:
            return taiToUtc(nsecs);
    }
    std::ostringstream os;
    os << "Unsupported scale " << scale;
    throw LSST_EXCEPT(lsst::pex::exceptions::InvalidParameterError, os.str());
}


#ifdef CAL_TO_JD

double calendarToJd(int year, int month, int day, int hour, int min, double sec) {
    if ( month <= 2 ) {
        year -= 1;
        month += 12;
    }
    int a = int(year/100);
    int b =  2 - a + int(a/4);

    int yy = 1582, mm = 10; //, d = 4;
    if (year < yy || (year == yy && month < mm) || (year == yy && month == mm && day <= 4)) {
        b = 0;
    }

    double jd = static_cast<int>(365.25*(year + 4716)) +
        static_cast<int>(30.6001*(month + 1)) + day + b - 1524.5;
    jd += hour/HOURS_PER_DAY + min/MIN_PER_DAY + sec/SEC_PER_DAY;

    return jd;
}

#endif // CAL_TO_JD
} // end anonymous namespace


namespace lsst {
namespace daf {
namespace base {

void DateTime::setNsecsFromMjd(double mjd, Timescale scale) {

    if (mjd > EPOCH_IN_MJD + MAX_DAYS) {
        throw LSST_EXCEPT(
                          lsst::pex::exceptions::DomainError,
                          (boost::format("MJD too far in the future: %1%") % mjd).str());
    }
    if (mjd < EPOCH_IN_MJD - MAX_DAYS) {
        throw LSST_EXCEPT(
                          lsst::pex::exceptions::DomainError,
                          (boost::format("MJD too far in the past: %1%") % mjd).str());
    }
    _nsecs = nsecAnyToTai(static_cast<long long>((mjd - EPOCH_IN_MJD) * NSEC_PER_DAY), scale);
}

void DateTime::setNsecsFromJd(double jd, Timescale scale) {
    setNsecsFromMjd(jd - MJD_TO_JD, scale);
}

void DateTime::setNsecsFromEpoch(double epoch, Timescale scale) {
    setNsecsFromMjd(365.25*(epoch - 2000.0) + JD2000 - MJD_TO_JD, scale);
}

DateTime::DateTime() :
    _nsecs(DateTime::invalid_nsecs)
{ }

DateTime::DateTime(long long nsecs, Timescale scale) :
    _nsecs(nsecAnyToTai(nsecs, scale))
{ }

DateTime::DateTime(double date, DateSystem system, Timescale scale) {
    switch (system) {
      case MJD:
        setNsecsFromMjd(date, scale);
        break;
      case JD:
        setNsecsFromJd(date, scale);
        break;
      case EPOCH:
        setNsecsFromEpoch(date, scale);
        break;
      default:
        throw LSST_EXCEPT(pexEx::InvalidParameterError, "DateSystem must be MJD, JD, or EPOCH");
        break;
    }
}

DateTime::DateTime(int year, int month, int day, int hr, int min, int sec, Timescale scale) {
    int const minYear = 1902;
    int const maxYear = 2261;
    if ((year < minYear) || (year > maxYear)) {
        throw LSST_EXCEPT(
            lsst::pex::exceptions::DomainError,
            (boost::format("Year = %d out of range [%04d, %04d]") % year % minYear % maxYear).str());
    }

    struct tm tm;
    tm.tm_year = year - 1900;
    tm.tm_mon = month - 1;
    tm.tm_mday = day;
    tm.tm_hour = hr;
    tm.tm_min = min;
    tm.tm_sec = sec;
    tm.tm_wday = 0;
    tm.tm_yday = 0;
    tm.tm_isdst = 0;
    tm.tm_gmtoff = 0;

    // Convert to seconds since the epoch, correcting to UTC.
    // Although timegm() is non-standard, it is a commonly-supported
    // extension and is much safer/more reliable than mktime(3) in that
    // it doesn't try to deal with the anomalies of local time zones.
    time_t secs = timegm(&tm);

    // long long nsecs will blow out beyond 1677-09-21T00:00:00 and 2262-04-12T00:00:00
    // (refering to the values of EPOCH_IN_MJD +/- MAX_DAYS ... exceeds 64 bits.)
    // On older machines a tm struct is only 32 bits, and saturates at:
    //    low end - 1901-12-13, 20:45:52
    //    hi end  - 2038-01-19, 03:14:07
    // On newer machines the upper limit is a date in 2262, but the low end is unchanged,
    // and a unit test will show the problem for dates later than 2038-01-19

    // timegm returns -1 on error, but the date at unix epoch -1 second also returns a valid value of -1,
    // so be sure to test for that

    if (secs == -1) {
        bool isBad = true;  // assume the worst
        if (year == 1969) {
            // date may be the one date at which unix sec = -1; try a different year
            tm.tm_year = 70;
            if (timegm(&tm) != -1) {
                isBad = false;
            }
        }
        if (isBad) {
            throw LSST_EXCEPT(
                lsst::pex::exceptions::DomainError,
                (boost::format("Unconvertible date: %04d-%02d-%02dT%02d:%02d:%02d")
                 % year % month % day % hr % min % sec).str());
        }
    }

    _nsecs = nsecAnyToTai(secs * LL_NSEC_PER_SEC, scale);
}

DateTime::DateTime(std::string const& iso8601, Timescale scale) {
    boost::regex re;
    if (scale == UTC) {
        // time zone "Z" required
        re = boost::regex("(\\d{4})-?(\\d{2})-?(\\d{2})" "T"
                          "(\\d{2}):?(\\d{2}):?(\\d{2})" "([.,](\\d*))?" "Z");
    } else {
        // no time zone character accepted
        re = boost::regex("(\\d{4})-?(\\d{2})-?(\\d{2})" "T"
                          "(\\d{2}):?(\\d{2}):?(\\d{2})" "([.,](\\d*))?");
    }
    boost::smatch matches;
    if (!regex_match(iso8601, matches, re)) {
        throw LSST_EXCEPT(lsst::pex::exceptions::DomainError,
                          "Not in acceptable ISO8601 format: " + iso8601);
    }
    // determine TAI nsec truncated to integer seconds
    // by constructing a DateTime from year, month, day...
    DateTime dt(atoi(matches.str(1).c_str()), atoi(matches.str(2).c_str()),
                atoi(matches.str(3).c_str()), atoi(matches.str(4).c_str()),
                atoi(matches.str(5).c_str()), atoi(matches.str(6).c_str()),
                scale);
    _nsecs = dt._nsecs;
    // add fractional seconds, if any
    if (matches[7].matched) {
        std::string frac = matches.str(8);
        int places = frac.size();
        if (places > 9) { // truncate fractional nanosec
            frac.erase(9);
        }
        int value = atoi(frac.c_str());
        while (places < 9) {
            value *= 10;
            ++places;
        }
        _nsecs += value;
    }
}

double DateTime::get(DateSystem system, Timescale scale) const {
    _assertValid();
    switch (system) {
      case MJD:
        return _getMjd(scale);
        break;
      case JD:
        return _getJd(scale);
        break;
      case EPOCH:
        return _getEpoch(scale);
        break;
      default:
        throw LSST_EXCEPT(pexEx::InvalidParameterError, "DateSystem must be MJD, JD, or EPOCH");
        break;
    }
}

long long DateTime::nsecs(Timescale scale) const {
    if (!isValid()) {
        // return the same invalid value for all time scales
        return DateTime::invalid_nsecs;
    }
    return nsecTaiToAny(_nsecs, scale);
}

double DateTime::_getMjd(Timescale scale) const {
    _assertValid();
    double nsecs = nsecTaiToAny(_nsecs, scale);
    return nsecs / NSEC_PER_DAY + EPOCH_IN_MJD;
}

double DateTime::_getJd(Timescale scale) const {
    return _getMjd(scale) + MJD_TO_JD;
}

double DateTime::_getEpoch(Timescale scale) const {
    return 2000.0 + (_getJd(scale) - JD2000)/365.25;
}

struct tm DateTime::gmtime(Timescale scale) const {
    _assertValid();
    struct tm gmt;
    long long nsecs = nsecTaiToAny(_nsecs, scale);
    // Round to negative infinity
    long long frac = nsecs % LL_NSEC_PER_SEC;
    if (nsecs < 0 && frac < 0) {
        nsecs -= LL_NSEC_PER_SEC + frac;
    }
    else {
        nsecs -= frac;
    }
    time_t secs = static_cast<time_t>(nsecs / LL_NSEC_PER_SEC);
    gmtime_r(&secs, &gmt);
    return gmt;
}

struct timespec DateTime::timespec(Timescale scale) const {
    _assertValid();
    struct timespec ts;
    long long nsecs = nsecTaiToAny(_nsecs, scale);
    ts.tv_sec = static_cast<time_t>(nsecs / LL_NSEC_PER_SEC);
    ts.tv_nsec = static_cast<int>(nsecs % LL_NSEC_PER_SEC);
    return ts;
}

struct timeval DateTime::timeval(Timescale scale) const {
    _assertValid();
    struct timeval tv;
    long long nsecs = nsecTaiToAny(_nsecs, scale);
    tv.tv_sec = static_cast<time_t>(nsecs / LL_NSEC_PER_SEC);
    tv.tv_usec = static_cast<int>((nsecs % LL_NSEC_PER_SEC) / 1000);
    return tv;
}

std::string DateTime::toString(Timescale scale) const {
    _assertValid();
    struct tm gmt(this->gmtime(scale));

    long long fracnsecs = nsecTaiToAny(_nsecs, scale) % LL_NSEC_PER_SEC;
    if (fracnsecs < 0) {
        fracnsecs += LL_NSEC_PER_SEC;
    }
    auto fmtStr = scale == UTC ? "%04d-%02d-%02dT%02d:%02d:%02d.%09dZ"
                               : "%04d-%02d-%02dT%02d:%02d:%02d.%09d";
    return (boost::format(fmtStr) %
            (gmt.tm_year + 1900) % (gmt.tm_mon + 1) % gmt.tm_mday %
            gmt.tm_hour % gmt.tm_min % gmt.tm_sec % fracnsecs).str();
}

bool DateTime::operator==(DateTime const& rhs) const {
    return _nsecs == rhs._nsecs;
}

DateTime DateTime::now(void) {
    struct timeval tv;
    int ret = gettimeofday(&tv, 0);
    if (ret != 0) {
        throw LSST_EXCEPT(lsst::pex::exceptions::RuntimeError,
                          "Unable to get current time");
    }
    long long nsecs = tv.tv_sec * LL_NSEC_PER_SEC + tv.tv_usec * 1000LL;
    return DateTime(nsecs, DateTime::UTC);
}

void DateTime::initializeLeapSeconds(std::string const& leapString) {
    Leap l;
    leapSecTable.clear();
    boost::regex re("^\\d{4}.*?=JD\\s*([\\d.]+)\\s+TAI-UTC=\\s+([\\d.]+)\\s+S"
                    " \\+ \\(MJD - ([\\d.]+)\\) X ([\\d.]+)\\s*S$");
    for (boost::cregex_iterator i = make_regex_iterator(leapString.c_str(), re);
         i != boost::cregex_iterator(); ++i) {
        double mjdUtc = strtod((*i)[1].first, 0) - MJD_TO_JD;
        l.offset = strtod((*i)[2].first, 0);
        l.mjdRef = strtod((*i)[3].first, 0);
        l.drift = strtod((*i)[4].first, 0);
        l.whenUtc = static_cast<long long>(
            (mjdUtc - EPOCH_IN_MJD) * NSEC_PER_DAY);
        l.whenTai = l.whenUtc + static_cast<long long>(
            1.0e9 * (l.offset + (mjdUtc - l.mjdRef) * l.drift));
        leapSecTable.push_back(l);
    }
}

}}} // namespace lsst::daf::base