#include "erfa.h" int eraDat(int iy, int im, int id, double fd, double *deltat ) /* ** - - - - - - - ** e r a 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 : ** : : ** :__________________________________________: ** ** 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: ** eraCal2jd Gregorian calendar to JD ** ** Copyright (C) 2013-2017, NumFOCUS Foundation. ** Derived, with permission, from the SOFA library. See notes at end of file. */ { /* Release year for this version of eraDat */ enum { IYV = 2016}; /* 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 = eraCal2jd(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) 2013-2017, 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. 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