LeapSeconds.cc

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#include <time.h>
#include <stdlib.h>
#include <utl/UTCDate.h>
#include <utl/LeapSeconds.h>

using namespace utl;
using namespace std;


bool
LeapSeconds::ConvertGPSToUnix(const unsigned long gpsSecond, time_t& unixSecond)
  const
{
  bool leap = false;
  GPSToUnixIterator low = fGPSToUnixLeaps.lower_bound(gpsSecond);
  if (low != fGPSToUnixLeaps.end())
    leap = (low->first == gpsSecond && low->second.first == 1);
  --low;
  unixSecond = fGPSEpochInUnixSeconds + gpsSecond + low->second.second;
  return leap;
}


void
LeapSeconds::ConvertUnixToGPS(const time_t unixSecond, unsigned long& gpsSecond)
  const
{
  UnixToGPSIterator up = fUnixToGPSLeaps.upper_bound(unixSecond);
  --up;
  gpsSecond = unixSecond - fGPSEpochInUnixSeconds + up->second;
}


void
LeapSeconds::Init()
{
  fGPSEpochInUnixSeconds = UTCDate::GetGPSEpoch().GetUnixSecond();

  struct DateLeap {
    UTCDate fNextDay; // day after the leap second
    int fLeap;        // +1 or -1 correction
  };

  /*
    Leap second is added before this date, e.g. the 1988-Jan-1 leap
    second extends the previous day for one second, so the last second
    of the day is 1987-Dec-1-T23:59:60, next is 1988-Jan-1-T00:00:00.

    Do not add leap seconds before the GPS epoch (1980-Jan-6)!
  */
  const DateLeap leaps[] = {
    { UTCDate(1981, UTCDate::eJul, 1), +1 },
    { UTCDate(1982, UTCDate::eJul, 1), +1 },
    { UTCDate(1983, UTCDate::eJul, 1), +1 },
    { UTCDate(1985, UTCDate::eJul, 1), +1 },
    { UTCDate(1988, UTCDate::eJan, 1), +1 },
    { UTCDate(1990, UTCDate::eJan, 1), +1 },
    { UTCDate(1991, UTCDate::eJan, 1), +1 },
    { UTCDate(1992, UTCDate::eJul, 1), +1 },
    { UTCDate(1993, UTCDate::eJul, 1), +1 },
    { UTCDate(1994, UTCDate::eJul, 1), +1 },
    { UTCDate(1996, UTCDate::eJan, 1), +1 },
    { UTCDate(1997, UTCDate::eJul, 1), +1 },
    { UTCDate(1999, UTCDate::eJan, 1), +1 },
    { UTCDate(2006, UTCDate::eJan, 1), +1 },
    { UTCDate(2009, UTCDate::eJan, 1), +1 },
    { UTCDate(2012, UTCDate::eJul, 1), +1 },
    { UTCDate(2015, UTCDate::eJul, 1), +1 },
    { UTCDate(2017, UTCDate::eJan, 1), +1 }
  };

  const int n = sizeof(leaps) / sizeof(DateLeap);

  int totalLeaps = 0;
  fGPSToUnixLeaps[0] = make_pair(0, 0);
  fUnixToGPSLeaps[0] = 0;

  for (int i = 0; i < n; ++i) {
    const time_t unixSecond = leaps[i].fNextDay.GetUnixSecond();
    const unsigned long gpsSecond = unixSecond - fGPSEpochInUnixSeconds + totalLeaps;
    const int leap = leaps[i].fLeap;
    totalLeaps += leap;
    fGPSToUnixLeaps[gpsSecond] = make_pair(leap, -totalLeaps);
    fUnixToGPSLeaps[unixSecond] = totalLeaps;
  }
}


void
LeapSeconds::Dump()
  const
{
  cout << "GPS->Unix\n";
  for (GPSToUnixIterator it = fGPSToUnixLeaps.begin();
       it != fGPSToUnixLeaps.end(); ++it)
    cout << it->first << ": "
         << it->second.first << ' ' << it->second.second << '\n';
  cout << "Unix->GPS\n";
  for (UnixToGPSIterator it = fUnixToGPSLeaps.begin();
       it != fUnixToGPSLeaps.end(); ++it)
    cout << it->first << " (" << (it->first - fGPSEpochInUnixSeconds) << "): "
         << it->second << '\n';
}


void
LeapSeconds::SetUTC()
{
  const char* const tz = getenv("TZ");
  if (tz)
    fTZ = new string(tz);
  setenv("TZ", "", 1);
  tzset();
}


void
LeapSeconds::UnsetUTC()
{
  if (fTZ) {
    setenv("TZ", fTZ->c_str(), 1);
    delete fTZ;
    fTZ = 0;
  } else
    unsetenv("TZ");
  tzset();
}