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Diffstat (limited to 'ast/erfa/d2dtf.c')
| -rw-r--r-- | ast/erfa/d2dtf.c | 245 |
1 files changed, 245 insertions, 0 deletions
diff --git a/ast/erfa/d2dtf.c b/ast/erfa/d2dtf.c new file mode 100644 index 0000000..4476970 --- /dev/null +++ b/ast/erfa/d2dtf.c @@ -0,0 +1,245 @@ +#include "erfa.h" +#include <string.h> + +int eraD2dtf(const char *scale, int ndp, double d1, double d2, + int *iy, int *im, int *id, int ihmsf[4]) +/* +** - - - - - - - - - +** e r a D 2 d t f +** - - - - - - - - - +** +** Format for output a 2-part Julian Date (or in the case of UTC a +** quasi-JD form that includes special provision for leap seconds). +** +** Given: +** scale char[] time scale ID (Note 1) +** ndp int resolution (Note 2) +** d1,d2 double time as a 2-part Julian Date (Notes 3,4) +** +** Returned: +** iy,im,id int year, month, day in Gregorian calendar (Note 5) +** ihmsf int[4] hours, minutes, seconds, fraction (Note 1) +** +** Returned (function value): +** int status: +1 = dubious year (Note 5) +** 0 = OK +** -1 = unacceptable date (Note 6) +** +** Notes: +** +** 1) scale identifies the time scale. Only the value "UTC" (in upper +** case) is significant, and enables handling of leap seconds (see +** Note 4). +** +** 2) ndp is the number of decimal places in the seconds field, and can +** have negative as well as positive values, such as: +** +** ndp resolution +** -4 1 00 00 +** -3 0 10 00 +** -2 0 01 00 +** -1 0 00 10 +** 0 0 00 01 +** 1 0 00 00.1 +** 2 0 00 00.01 +** 3 0 00 00.001 +** +** The limits are platform dependent, but a safe range is -5 to +9. +** +** 3) d1+d2 is Julian Date, apportioned in any convenient way between +** the two arguments, for example where d1 is the Julian Day Number +** and d2 is the fraction of a day. In the case of UTC, where the +** use of JD is problematical, special conventions apply: see the +** next note. +** +** 4) JD cannot unambiguously represent UTC during a leap second unless +** special measures are taken. The ERFA internal convention is that +** the quasi-JD day represents UTC days whether the length is 86399, +** 86400 or 86401 SI seconds. In the 1960-1972 era there were +** smaller jumps (in either direction) each time the linear UTC(TAI) +** expression was changed, and these "mini-leaps" are also included +** in the ERFA convention. +** +** 5) The warning status "dubious year" flags UTCs that predate the +** introduction of the time scale or that are too far in the future +** to be trusted. See eraDat for further details. +** +** 6) For calendar conventions and limitations, see eraCal2jd. +** +** Called: +** eraJd2cal JD to Gregorian calendar +** eraD2tf decompose days to hms +** eraDat delta(AT) = TAI-UTC +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + int leap; + char s; + int iy1, im1, id1, js, iy2, im2, id2, ihmsf1[4], i; + double a1, b1, fd, dat0, dat12, w, dat24, dleap; + + +/* The two-part JD. */ + a1 = d1; + b1 = d2; + +/* Provisional calendar date. */ + js = eraJd2cal(a1, b1, &iy1, &im1, &id1, &fd); + if ( js ) return -1; + +/* Is this a leap second day? */ + leap = 0; + if ( ! strcmp(scale,"UTC") ) { + + /* TAI-UTC at 0h today. */ + js = eraDat(iy1, im1, id1, 0.0, &dat0); + if ( js < 0 ) return -1; + + /* TAI-UTC at 12h today (to detect drift). */ + js = eraDat(iy1, im1, id1, 0.5, &dat12); + if ( js < 0 ) return -1; + + /* TAI-UTC at 0h tomorrow (to detect jumps). */ + js = eraJd2cal(a1+1.5, b1-fd, &iy2, &im2, &id2, &w); + if ( js ) return -1; + js = eraDat(iy2, im2, id2, 0.0, &dat24); + if ( js < 0 ) return -1; + + /* Any sudden change in TAI-UTC (seconds). */ + dleap = dat24 - (2.0*dat12 - dat0); + + /* If leap second day, scale the fraction of a day into SI. */ + leap = (dleap != 0.0); + if (leap) fd += fd * dleap/ERFA_DAYSEC; + } + +/* Provisional time of day. */ + eraD2tf ( ndp, fd, &s, ihmsf1 ); + +/* Has the (rounded) time gone past 24h? */ + if ( ihmsf1[0] > 23 ) { + + /* Yes. We probably need tomorrow's calendar date. */ + js = eraJd2cal(a1+1.5, b1-fd, &iy2, &im2, &id2, &w); + if ( js ) return -1; + + /* Is today a leap second day? */ + if ( ! leap ) { + + /* No. Use 0h tomorrow. */ + iy1 = iy2; + im1 = im2; + id1 = id2; + ihmsf1[0] = 0; + ihmsf1[1] = 0; + ihmsf1[2] = 0; + + } else { + + /* Yes. Are we past the leap second itself? */ + if ( ihmsf1[2] > 0 ) { + + /* Yes. Use tomorrow but allow for the leap second. */ + iy1 = iy2; + im1 = im2; + id1 = id2; + ihmsf1[0] = 0; + ihmsf1[1] = 0; + ihmsf1[2] = 0; + + } else { + + /* No. Use 23 59 60... today. */ + ihmsf1[0] = 23; + ihmsf1[1] = 59; + ihmsf1[2] = 60; + } + + /* If rounding to 10s or coarser always go up to new day. */ + if ( ndp < 0 && ihmsf1[2] == 60 ) { + iy1 = iy2; + im1 = im2; + id1 = id2; + ihmsf1[0] = 0; + ihmsf1[1] = 0; + ihmsf1[2] = 0; + } + } + } + +/* Results. */ + *iy = iy1; + *im = im1; + *id = id1; + for ( i = 0; i < 4; i++ ) { + ihmsf[i] = ihmsf1[i]; + } + +/* Status. */ + return js; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |