1 // sg_time.cxx -- data structures and routines for managing time related stuff.
3 // Written by Curtis Olson, started August 1997.
5 // Copyright (C) 1997 Curtis L. Olson - http://www.flightgear.org/~curt
7 // This library is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU Library General Public
9 // License as published by the Free Software Foundation; either
10 // version 2 of the License, or (at your option) any later version.
12 // This library is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 // Library General Public License for more details.
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, write to the Free Software
19 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
25 # include <simgear_config.h>
28 #include <simgear/compiler.h>
30 #include <errno.h> // for errno
39 #ifdef HAVE_SYS_TIME_H
40 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
42 #ifdef HAVE_SYS_TIMEB_H
43 # include <sys/timeb.h> // for ftime() and struct timeb
46 # include <unistd.h> // for gettimeofday()
49 #include <math.h> // for NAN
51 #include <simgear/constants.h>
52 #include <simgear/debug/logstream.hxx>
53 #include <simgear/misc/sg_path.hxx>
55 #include "sg_time.hxx"
57 #include "lowleveltime.h"
59 #define DEGHR(x) ((x)/15.)
60 #define RADHR(x) DEGHR(x*SGD_RADIANS_TO_DEGREES)
64 static const double MJD0 = 2415020.0;
65 static const double J2000 = 2451545.0 - MJD0;
66 static const double SIDRATE = 0.9972695677;
68 // tzContainer stores all the current Timezone control points/
69 std::auto_ptr<SGTimeZoneContainer> static_tzContainer;
71 void SGTime::init( const SGGeod& location, const SGPath& root, time_t init_time )
78 cur_time = time(NULL);
81 SG_LOG( SG_EVENT, SG_DEBUG,
82 "Current greenwich mean time = " << asctime(gmtime(&cur_time)));
83 SG_LOG( SG_EVENT, SG_DEBUG,
84 "Current local time = " << asctime(localtime(&cur_time)));
86 if ( !root.isNull()) {
87 if (!static_tzContainer.get()) {
89 zone.append( "zone.tab" );
90 SG_LOG( SG_EVENT, SG_INFO, "Reading timezone info from: "
92 static_tzContainer.reset(new SGTimeZoneContainer( zone.c_str() ));
95 SGTimeZone* nearestTz = static_tzContainer->getNearest(location);
98 name.append( nearestTz->getDescription() );
99 zonename = name.str();
100 SG_LOG( SG_EVENT, SG_DEBUG, "Using zonename = " << zonename );
106 SGTime::SGTime( const SGGeod& location, const SGPath& root,
109 init(location, root, init_time);
112 SGTime::SGTime( const SGPath& root ) {
113 init( SGGeod(), root, 0 );
118 init( SGGeod(), SGPath(), 0 );
127 // given Julian Date and Longitude (decimal degrees West) compute
128 // Local Sidereal Time, in decimal hours.
130 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
131 static double sidereal_precise( double mjd, double lng )
133 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
136 // convert to required internal units
137 lng *= SGD_DEGREES_TO_RADIANS;
139 // compute LST and print
140 double gst = sgTimeCalcGST( mjd );
141 double lst = gst - RADHR( lng );
142 lst -= 24.0 * floor( lst / 24.0 );
143 // printf ("%7.4f\n", lstTmp);
149 // return a courser but cheaper estimate of sidereal time
150 static double sidereal_course( time_t cur_time, const struct tm *gmt, double lng )
152 time_t start_gmt, now;
153 double diff, part, days, hours, lstTmp;
156 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
158 diff = (now - start_gmt) / (3600.0 * 24.0);
160 part = fmod(diff, 1.0);
162 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
164 lstTmp = (days - lng)/15.0 + hours - 12;
166 while ( lstTmp < 0.0 ) {
173 // Update the time related variables
174 void SGTime::update( const SGGeod& location, time_t ct, long int warp )
176 double gst_precise, gst_course;
182 // get current Unix calendar time (in seconds)
183 // warp += warp_delta;
185 cur_time = ct + warp;
187 cur_time = time(NULL) + warp;
190 // get GMT break down for current time
192 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
193 // calculate modified Julian date starting with current
194 mjd = sgTimeCurrentMJD( ct, warp );
196 // add in partial day
197 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
198 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
200 // convert "back" to Julian date + partial day (as a fraction of one)
203 // printf(" Current Longitude = %.3f\n", FG_Longitude * SGD_RADIANS_TO_DEGREES);
205 // Calculate local side real time
206 if ( gst_diff < -100.0 ) {
207 // first time through do the expensive calculation & cheap
208 // calculation to get the difference.
209 SG_LOG( SG_EVENT, SG_DEBUG, " First time, doing precise gst" );
210 gst_precise = gst = sidereal_precise( mjd, 0.00 );
211 gst_course = sidereal_course( cur_time, gmt, 0.00 );
213 gst_diff = gst_precise - gst_course;
215 lst = sidereal_course( cur_time, gmt,
216 -location.getLongitudeDeg() ) + gst_diff;
218 // course + difference should drift off very slowly
219 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
220 lst = sidereal_course( cur_time, gmt,
221 -location.getLongitudeDeg() ) + gst_diff;
226 // Given lon/lat, update timezone information and local_offset
227 void SGTime::updateLocal( const SGGeod& aLocation, const string& root ) {
228 SGGeod location(aLocation);
229 if (!aLocation.isValid()) {
234 time_t aircraftLocalTime;
235 SGTimeZone* nearestTz = static_tzContainer->getNearest(location);
237 zone.append ( nearestTz->getDescription() );
238 zonename = zone.str();
240 //Avoid troubles when zone.tab hasn't got the right line endings
241 if (zonename[zonename.size()-1] == '\r')
243 zonename[zonename.size()-1]=0;
244 zone.set( zonename );
247 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
248 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
249 local_offset = aircraftLocalTime - currGMT;
250 // cout << "Using " << local_offset << " as local time offset Timezone is "
251 // << zonename << endl;
255 // given a date in months, mn, days, dy, years, yr, return the
256 // modified Julian date (number of days elapsed since 1900 jan 0.5),
257 // mjd. Adapted from Xephem.
258 double sgTimeCalcMJD(int mn, double dy, int yr) {
261 // internal book keeping data
262 static double last_mjd, last_dy;
263 static int last_mn, last_yr;
268 if (mn == last_mn && yr == last_yr && dy == last_dy) {
273 y = (yr < 0) ? yr + 1 : yr;
279 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
288 c = (long)((365.25*y) - 0.75) - 694025L;
290 c = (long)(365.25*y) - 694025L;
293 d = (int)(30.6001*(m+1));
295 mjd = b + c + d + dy - 0.5;
306 // return the current modified Julian date (number of days elapsed
307 // since 1900 jan 0.5), mjd.
308 double sgTimeCurrentMJD( time_t ct, long int warp ) {
310 struct tm m_gmt; // copy of system gmtime(&time_t) structure
311 struct tm *gmt = &m_gmt;
313 // get current Unix calendar time (in seconds)
314 // warp += warp_delta;
317 cur_time = ct + warp;
319 cur_time = time(NULL) + warp;
322 // get GMT break down for current time
323 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
325 // calculate modified Julian date
326 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
327 // (int)(t->gmt->tm_year + 1900));
328 double mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
329 (int)(gmt->tm_year + 1900) );
335 // given an mjd, calculate greenwich mean sidereal time, gst
336 double sgTimeCalcGST( double mjd ) {
339 double day = floor(mjd-0.5)+0.5;
340 double hr = (mjd-day)*24.0;
343 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
344 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
346 gst = (1.0/SIDRATE)*hr + x;
352 #if defined( HAVE_TIMEGM )
353 // ignore this function
354 #elif defined( MK_TIME_IS_GMT )
355 // ignore this function
356 #else // ! defined ( MK_TIME_IS_GMT )
358 // Fix up timezone if using ftime()
359 static long int fix_up_timezone( long int timezone_orig ) {
360 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
361 // ftime() needs a little extra help finding the current timezone
362 struct timeb current;
364 return( current.timezone * 60 );
366 return( timezone_orig );
372 /******************************************************************
373 * The following are some functions that were included as SGTime
374 * members, although they currently don't make use of any of the
375 * class's variables. Maybe this'll change in the future
376 *****************************************************************/
378 // Return time_t for Sat Mar 21 12:00:00 GMT
380 // On many systems it is ambiguous if mktime() assumes the input is in
381 // GMT, or local timezone. To address this, a new function called
382 // timegm() is appearing. It works exactly like mktime() but
383 // explicitely interprets the input as GMT.
385 // timegm() is available and documented under FreeBSD. It is
386 // available, but completely undocumented on my current Debian 2.1
389 // In the absence of timegm() we have to guess what mktime() might do.
391 // Many older BSD style systems have a mktime() that assumes the input
392 // time in GMT. But FreeBSD explicitly states that mktime() assumes
395 // The mktime() on many SYSV style systems (such as Linux) usually
396 // returns its result assuming you have specified the input time in
397 // your local timezone. Therefore, in the absence if timegm() you
398 // have to go to extra trouble to convert back to GMT.
400 // If you are having problems with incorrectly positioned astronomical
401 // bodies, this is a really good place to start looking.
403 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
413 mt.tm_isdst = -1; // let the system determine the proper time zone
415 // For now we assume that if daylight is not defined in
416 // /usr/include/time.h that we have a machine with a mktime() that
417 // assumes input is in GMT ... this only matters if we are
418 // building on a system that does not have timegm()
419 #if !defined(HAVE_DAYLIGHT)
420 # define MK_TIME_IS_GMT 1
423 #if defined( HAVE_TIMEGM )
424 return ( timegm(&mt) );
425 #elif defined( MK_TIME_IS_GMT )
426 time_t ret = mktime(&mt);
432 // This is necessary as some mktime() calls may
433 // try to access the system timezone files
434 // if this open fails errno is set to 2
435 // CYGWIN for one does this
437 // perror( "sgTimeGetGMT()" );
441 // reset errno in any event.
445 #else // ! defined ( MK_TIME_IS_GMT )
447 // timezone seems to work as a proper offset for Linux & Solaris
448 # if defined( __linux__ ) || defined(__sun) ||defined(__CYGWIN__)
449 # define TIMEZONE_OFFSET_WORKS 1
452 #if defined(__CYGWIN__)
453 #define TIMEZONE _timezone
455 #define TIMEZONE timezone
458 time_t start = mktime(&mt);
460 SG_LOG( SG_EVENT, SG_DEBUG, "start1 = " << start );
461 // the ctime() call can screw up time progression on some versions
463 // fgPrintf( SG_EVENT, SG_DEBUG, "start2 = %s", ctime(&start));
464 SG_LOG( SG_EVENT, SG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
466 TIMEZONE = fix_up_timezone( TIMEZONE );
468 # if defined( TIMEZONE_OFFSET_WORKS )
469 SG_LOG( SG_EVENT, SG_DEBUG,
470 "start = " << start << ", timezone = " << TIMEZONE );
471 return( start - TIMEZONE );
472 # else // ! defined( TIMEZONE_OFFSET_WORKS )
474 daylight = mt.tm_isdst;
475 if ( daylight > 0 ) {
477 } else if ( daylight < 0 ) {
478 SG_LOG( SG_EVENT, SG_WARN,
479 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
482 long int offset = -(TIMEZONE / 3600 - daylight);
484 SG_LOG( SG_EVENT, SG_DEBUG, " Raw time zone offset = " << TIMEZONE );
485 SG_LOG( SG_EVENT, SG_DEBUG, " Daylight Savings = " << daylight );
486 SG_LOG( SG_EVENT, SG_DEBUG, " Local hours from GMT = " << offset );
488 long int start_gmt = start - TIMEZONE + (daylight * 3600);
490 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (CST) = " << start );
492 return ( start_gmt );
493 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
494 #endif // ! defined ( MK_TIME_IS_GMT )
499 char* sgTimeFormatTime( const struct tm* p, char* buf )
501 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
502 p->tm_mon, p->tm_mday, p->tm_year,
503 p->tm_hour, p->tm_min, p->tm_sec);