d2tf.c

Go to the documentation of this file.

#include "erfa.h"

void eraD2tf(int ndp, double days, char *sign, int ihmsf[4])
/*
**  - - - - - - - -
**   e r a D 2 t f
**  - - - - - - - -
**
**  Decompose days to hours, minutes, seconds, fraction.
**
**  Given:
**     ndp     int     resolution (Note 1)
**     days    double  interval in days
**
**  Returned:
**     sign    char    '+' or '-'
**     ihmsf   int[4]  hours, minutes, seconds, fraction
**
**  Notes:
**
**  1) The argument ndp is interpreted as follows:
**
**     ndp         resolution
**      :      ...0000 00 00
**     -7         1000 00 00
**     -6          100 00 00
**     -5           10 00 00
**     -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
**      :            0 00 00.000...
**
**  2) The largest positive useful value for ndp is determined by the
**     size of days, the format of double on the target platform, and
**     the risk of overflowing ihmsf[3].  On a typical platform, for
**     days up to 1.0, the available floating-point precision might
**     correspond to ndp=12.  However, the practical limit is typically
**     ndp=9, set by the capacity of a 32-bit int, or ndp=4 if int is
**     only 16 bits.
**
**  3) The absolute value of days may exceed 1.0.  In cases where it
**     does not, it is up to the caller to test for and handle the
**     case where days is very nearly 1.0 and rounds up to 24 hours,
**     by testing for ihmsf[0]=24 and setting ihmsf[0-3] to zero.
**
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   int nrs, n;
   double rs, rm, rh, a, w, ah, am, as, af;

/* Handle sign. */
   *sign = (char) ( ( days >= 0.0 ) ? '+' : '-' );

/* Interval in seconds. */
   a = ERFA_DAYSEC * fabs(days);

/* Pre-round if resolution coarser than 1s (then pretend ndp=1). */
   if (ndp < 0) {
      nrs = 1;
      for (n = 1; n <= -ndp; n++) {
          nrs *= (n == 2 || n == 4) ? 6 : 10;
      }
      rs = (double) nrs;
      w = a / rs;
      a = rs * ERFA_DNINT(w);
   }

/* Express the unit of each field in resolution units. */
   nrs = 1;
   for (n = 1; n <= ndp; n++) {
      nrs *= 10;
   }
   rs = (double) nrs;
   rm = rs * 60.0;
   rh = rm * 60.0;

/* Round the interval and express in resolution units. */
   a = ERFA_DNINT(rs * a);

/* Break into fields. */
   ah = a / rh;
   ah = ERFA_DINT(ah);
   a -= ah * rh;
   am = a / rm;
   am = ERFA_DINT(am);
   a -= am * rm;
   as = a / rs;
   as = ERFA_DINT(as);
   af = a - as * rs;

/* Return results. */
   ihmsf[0] = (int) ah;
   ihmsf[1] = (int) am;
   ihmsf[2] = (int) as;
   ihmsf[3] = (int) af;

   return;

}
/*----------------------------------------------------------------------
**  
**  
**  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:
**  
**  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.
**  
*/