jdcalf.c

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#include "erfa.h"

int eraJdcalf(int ndp, double dj1, double dj2, int iymdf[4])
/*
**  - - - - - - - - - -
**   e r a J d c a l f
**  - - - - - - - - - -
**
**  Julian Date to Gregorian Calendar, expressed in a form convenient
**  for formatting messages:  rounded to a specified precision.
**
**  Given:
**     ndp       int      number of decimal places of days in fraction
**     dj1,dj2   double   dj1+dj2 = Julian Date (Note 1)
**
**  Returned:
**     iymdf     int[4]   year, month, day, fraction in Gregorian
**                        calendar
**
**  Returned (function value):
**               int      status:
**                          -1 = date out of range
**                           0 = OK
**                          +1 = NDP not 0-9 (interpreted as 0)
**
**  Notes:
**
**  1) The Julian Date is apportioned in any convenient way between
**     the arguments dj1 and dj2.  For example, JD=2450123.7 could
**     be expressed in any of these ways, among others:
**
**             dj1            dj2
**
**         2450123.7           0.0       (JD method)
**         2451545.0       -1421.3       (J2000 method)
**         2400000.5       50123.2       (MJD method)
**         2450123.5           0.2       (date & time method)
**
**  2) In early eras the conversion is from the "Proleptic Gregorian
**     Calendar";  no account is taken of the date(s) of adoption of
**     the Gregorian Calendar, nor is the AD/BC numbering convention
**     observed.
**
**  3) Refer to the function eraJd2cal.
**
**  4) NDP should be 4 or less if internal overflows are to be
**     avoided on machines which use 16-bit integers.
**
**  Called:
**     eraJd2cal    JD to Gregorian calendar
**
**  Reference:
**
**     Explanatory Supplement to the Astronomical Almanac,
**     P. Kenneth Seidelmann (ed), University Science Books (1992),
**     Section 12.92 (p604).
**
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   int j, js;
   double denom, d1, d2, f1, f2, f;

/* Denominator of fraction (e.g. 100 for 2 decimal places). */
   if ((ndp >= 0) && (ndp <= 9)) {
      j = 0;
      denom = pow(10.0, ndp);
   } else {
      j = 1;
      denom = 1.0;
   }

/* Copy the date, big then small, and realign to midnight. */
   if (dj1 >= dj2) {
      d1 = dj1;
      d2 = dj2;
   } else {
      d1 = dj2;
      d2 = dj1;
   }
   d2 -= 0.5;

/* Separate days and fractions. */
   f1 = fmod(d1, 1.0);
   f2 = fmod(d2, 1.0);
   d1 = floor(d1 - f1);
   d2 = floor(d2 - f2);

/* Round the total fraction to the specified number of places. */
   f = floor((f1+f2)*denom + 0.5) / denom;

/* Re-assemble the rounded date and re-align to noon. */
   d2 += f + 0.5;

/* Convert to Gregorian calendar. */
   js = eraJd2cal(d1, d2, &iymdf[0], &iymdf[1], &iymdf[2], &f);
   if (js == 0) {
      iymdf[3] = (int) (f * denom);
   } else {
      j = js;
   }

/* Return the status. */
   return j;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2015, 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:
**  
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**    notice, this list of conditions and the following disclaimer.
**  
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**    distribution.
**  
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