#include "sofa.h" int iauDat(int iy, int im, int id, double fd, double *deltat) /* ** - - - - - - - ** i a u D a t ** - - - - - - - ** ** For a given UTC date, calculate Delta(AT) = TAI-UTC. ** ** :------------------------------------------: ** : : ** : IMPORTANT : ** : : ** : A new version of this function must be : ** : produced whenever a new leap second is : ** : announced. There are four items to : ** : change on each such occasion: : ** : : ** : 1) A new line must be added to the set : ** : of statements that initialize the : ** : array "changes". : ** : : ** : 2) The constant IYV must be set to the : ** : current year. : ** : : ** : 3) The "Latest leap second" comment : ** : below must be set to the new leap : ** : second date. : ** : : ** : 4) The "This revision" comment, later, : ** : must be set to the current date. : ** : : ** : Change (2) must also be carried out : ** : whenever the function is re-issued, : ** : even if no leap seconds have been : ** : added. : ** : : ** : Latest leap second: 2016 December 31 : ** : : ** :__________________________________________: ** ** This function is part of the International Astronomical Union's ** SOFA (Standards Of Fundamental Astronomy) software collection. ** ** Status: user-replaceable support function. ** ** Given: ** iy int UTC: year (Notes 1 and 2) ** im int month (Note 2) ** id int day (Notes 2 and 3) ** fd double fraction of day (Note 4) ** ** Returned: ** deltat double TAI minus UTC, seconds ** ** Returned (function value): ** int status (Note 5): ** 1 = dubious year (Note 1) ** 0 = OK ** -1 = bad year ** -2 = bad month ** -3 = bad day (Note 3) ** -4 = bad fraction (Note 4) ** -5 = internal error (Note 5) ** ** Notes: ** ** 1) UTC began at 1960 January 1.0 (JD 2436934.5) and it is improper ** to call the function with an earlier date. If this is attempted, ** zero is returned together with a warning status. ** ** Because leap seconds cannot, in principle, be predicted in ** advance, a reliable check for dates beyond the valid range is ** impossible. To guard against gross errors, a year five or more ** after the release year of the present function (see the constant ** IYV) is considered dubious. In this case a warning status is ** returned but the result is computed in the normal way. ** ** For both too-early and too-late years, the warning status is +1. ** This is distinct from the error status -1, which signifies a year ** so early that JD could not be computed. ** ** 2) If the specified date is for a day which ends with a leap second, ** the TAI-UTC value returned is for the period leading up to the ** leap second. If the date is for a day which begins as a leap ** second ends, the TAI-UTC returned is for the period following the ** leap second. ** ** 3) The day number must be in the normal calendar range, for example ** 1 through 30 for April. The "almanac" convention of allowing ** such dates as January 0 and December 32 is not supported in this ** function, in order to avoid confusion near leap seconds. ** ** 4) The fraction of day is used only for dates before the ** introduction of leap seconds, the first of which occurred at the ** end of 1971. It is tested for validity (0 to 1 is the valid ** range) even if not used; if invalid, zero is used and status -4 ** is returned. For many applications, setting fd to zero is ** acceptable; the resulting error is always less than 3 ms (and ** occurs only pre-1972). ** ** 5) The status value returned in the case where there are multiple ** errors refers to the first error detected. For example, if the ** month and day are 13 and 32 respectively, status -2 (bad month) ** will be returned. The "internal error" status refers to a ** case that is impossible but causes some compilers to issue a ** warning. ** ** 6) In cases where a valid result is not available, zero is returned. ** ** References: ** ** 1) For dates from 1961 January 1 onwards, the expressions from the ** file ftp://maia.usno.navy.mil/ser7/tai-utc.dat are used. ** ** 2) The 5ms timestep at 1961 January 1 is taken from 2.58.1 (p87) of ** the 1992 Explanatory Supplement. ** ** Called: ** iauCal2jd Gregorian calendar to JD ** ** This revision: 2020 May 31 ** ** SOFA release 2021-01-25 ** ** Copyright (C) 2021 IAU SOFA Board. See notes at end. */ { /* Release year for this version of iauDat */ enum { IYV = 2020}; /* Reference dates (MJD) and drift rates (s/day), pre leap seconds */ static const double drift[][2] = { { 37300.0, 0.0012960 }, { 37300.0, 0.0012960 }, { 37300.0, 0.0012960 }, { 37665.0, 0.0011232 }, { 37665.0, 0.0011232 }, { 38761.0, 0.0012960 }, { 38761.0, 0.0012960 }, { 38761.0, 0.0012960 }, { 38761.0, 0.0012960 }, { 38761.0, 0.0012960 }, { 38761.0, 0.0012960 }, { 38761.0, 0.0012960 }, { 39126.0, 0.0025920 }, { 39126.0, 0.0025920 } }; /* Number of Delta(AT) expressions before leap seconds were introduced */ enum { NERA1 = (int) (sizeof drift / sizeof (double) / 2) }; /* Dates and Delta(AT)s */ static const struct { int iyear, month; double delat; } changes[] = { { 1960, 1, 1.4178180 }, { 1961, 1, 1.4228180 }, { 1961, 8, 1.3728180 }, { 1962, 1, 1.8458580 }, { 1963, 11, 1.9458580 }, { 1964, 1, 3.2401300 }, { 1964, 4, 3.3401300 }, { 1964, 9, 3.4401300 }, { 1965, 1, 3.5401300 }, { 1965, 3, 3.6401300 }, { 1965, 7, 3.7401300 }, { 1965, 9, 3.8401300 }, { 1966, 1, 4.3131700 }, { 1968, 2, 4.2131700 }, { 1972, 1, 10.0 }, { 1972, 7, 11.0 }, { 1973, 1, 12.0 }, { 1974, 1, 13.0 }, { 1975, 1, 14.0 }, { 1976, 1, 15.0 }, { 1977, 1, 16.0 }, { 1978, 1, 17.0 }, { 1979, 1, 18.0 }, { 1980, 1, 19.0 }, { 1981, 7, 20.0 }, { 1982, 7, 21.0 }, { 1983, 7, 22.0 }, { 1985, 7, 23.0 }, { 1988, 1, 24.0 }, { 1990, 1, 25.0 }, { 1991, 1, 26.0 }, { 1992, 7, 27.0 }, { 1993, 7, 28.0 }, { 1994, 7, 29.0 }, { 1996, 1, 30.0 }, { 1997, 7, 31.0 }, { 1999, 1, 32.0 }, { 2006, 1, 33.0 }, { 2009, 1, 34.0 }, { 2012, 7, 35.0 }, { 2015, 7, 36.0 }, { 2017, 1, 37.0 } }; /* Number of Delta(AT) changes */ enum { NDAT = (int) (sizeof changes / sizeof changes[0]) }; /* Miscellaneous local variables */ int j, i, m; double da, djm0, djm; /* Initialize the result to zero. */ *deltat = da = 0.0; /* If invalid fraction of a day, set error status and give up. */ if (fd < 0.0 || fd > 1.0) return -4; /* Convert the date into an MJD. */ j = iauCal2jd(iy, im, id, &djm0, &djm); /* If invalid year, month, or day, give up. */ if (j < 0) return j; /* If pre-UTC year, set warning status and give up. */ if (iy < changes[0].iyear) return 1; /* If suspiciously late year, set warning status but proceed. */ if (iy > IYV + 5) j = 1; /* Combine year and month to form a date-ordered integer... */ m = 12*iy + im; /* ...and use it to find the preceding table entry. */ for (i = NDAT-1; i >=0; i--) { if (m >= (12 * changes[i].iyear + changes[i].month)) break; } /* Prevent underflow warnings. */ if (i < 0) return -5; /* Get the Delta(AT). */ da = changes[i].delat; /* If pre-1972, adjust for drift. */ if (i < NERA1) da += (djm + fd - drift[i][0]) * drift[i][1]; /* Return the Delta(AT) value. */ *deltat = da; /* Return the status. */ return j; /*---------------------------------------------------------------------- ** ** Copyright (C) 2018 ** Standards Of Fundamental Astronomy Board ** of the International Astronomical Union. ** ** ===================== ** SOFA Software License ** ===================== ** ** NOTICE TO USER: ** ** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND ** CONDITIONS WHICH APPLY TO ITS USE. ** ** 1. The Software is owned by the IAU SOFA Board ("SOFA"). ** ** 2. Permission is granted to anyone to use the SOFA software for any ** purpose, including commercial applications, free of charge and ** without payment of royalties, subject to the conditions and ** restrictions listed below. ** ** 3. You (the user) may copy and distribute SOFA source code to others, ** and use and adapt its code and algorithms in your own software, ** on a world-wide, royalty-free basis. That portion of your ** distribution that does not consist of intact and unchanged copies ** of SOFA source code files is a "derived work" that must comply ** with the following requirements: ** ** a) Your work shall be marked or carry a statement that it ** (i) uses routines and computations derived by you from ** software provided by SOFA under license to you; and ** (ii) does not itself constitute software provided by and/or ** endorsed by SOFA. ** ** b) The source code of your derived work must contain descriptions ** of how the derived work is based upon, contains and/or differs ** from the original SOFA software. ** ** c) UNLIKE OTHER SOFA SOFTWARE, WHICH IS STRICTLY "READ ONLY", ** USERS ARE PERMITTED TO REPLACE THIS FUNCTION WITH ONE USING ** THE SAME NAME BUT DIFFERENT CODE. This is to allow use of ** locally supported mechanisms for keeping track of leap ** seconds, perhaps file or network based. It avoids the need ** for applications to be relinked periodically in order to pick ** up SOFA updates. ** ** d) The origin of the SOFA components of your derived work must ** not be misrepresented; you must not claim that you wrote the ** original software, nor file a patent application for SOFA ** software or algorithms embedded in the SOFA software. ** ** e) These requirements must be reproduced intact in any source ** distribution and shall apply to anyone to whom you have ** granted a further right to modify the source code of your ** derived work. ** ** Note that, as originally distributed, the SOFA software is ** intended to be a definitive implementation of the IAU standards, ** and consequently third-party modifications are discouraged. All ** variations, no matter how minor, must be explicitly marked as ** such, as explained above. ** ** 4. You shall not cause the SOFA software to be brought into ** disrepute, either by misuse, or use for inappropriate tasks, or ** by inappropriate modification. ** ** 5. The SOFA software is provided "as is" and SOFA makes no warranty ** as to its use or performance. SOFA does not and cannot warrant ** the performance or results which the user may obtain by using the ** SOFA software. SOFA makes no warranties, express or implied, as ** to non-infringement of third party rights, merchantability, or ** fitness for any particular purpose. In no event will SOFA be ** liable to the user for any consequential, incidental, or special ** damages, including any lost profits or lost savings, even if a ** SOFA representative has been advised of such damages, or for any ** claim by any third party. ** ** 6. The provision of any version of the SOFA software under the terms ** and conditions specified herein does not imply that future ** versions will also be made available under the same terms and ** conditions. * ** In any published work or commercial product which uses the SOFA ** software directly, acknowledgement (see www.iausofa.org) is ** appreciated. ** ** Correspondence concerning SOFA software should be addressed as ** follows: ** ** By email: sofa@ukho.gov.uk ** By post: IAU SOFA Center ** HM Nautical Almanac Office ** UK Hydrographic Office ** Admiralty Way, Taunton ** Somerset, TA1 2DN ** United Kingdom ** **--------------------------------------------------------------------*/ }