/* mpfr_reldiff -- compute relative difference of two floating-point numbers.

Copyright 2000-2001, 2004-2018 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.

This file is part of the GNU MPFR Library.

The GNU MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.

The GNU MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */

#include "mpfr-impl.h"

/* reldiff(b, c) = abs(b-c)/b */
void
mpfr_reldiff (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode)
{
  mpfr_t b_copy;

  if (MPFR_ARE_SINGULAR (b, c))
    {
      if (MPFR_IS_NAN(b) || MPFR_IS_NAN(c))
        {
          MPFR_SET_NAN(a);
          return;
        }
      else if (MPFR_IS_INF(b))
        {
          if (MPFR_IS_INF (c) && (MPFR_SIGN (c) == MPFR_SIGN (b)))
            MPFR_SET_ZERO(a);
          else
            MPFR_SET_NAN(a);
          return;
        }
      else if (MPFR_IS_INF(c))
        {
          MPFR_SET_SAME_SIGN (a, b);
          MPFR_SET_INF (a);
          return;
        }
      else if (MPFR_IS_ZERO(b)) /* reldiff = abs(c)/c = sign(c) */
        {
          mpfr_set_si (a, MPFR_INT_SIGN (c), rnd_mode);
          return;
        }
      /* Fall through */
    }

  if (a == b)
    {
      mpfr_init2 (b_copy, MPFR_PREC(b));
      mpfr_set (b_copy, b, MPFR_RNDN);
    }

  mpfr_sub (a, b, c, rnd_mode);
  mpfr_abs (a, a, rnd_mode); /* for compatibility with MPF */
  mpfr_div (a, a, (a == b) ? b_copy : b, rnd_mode);

  if (a == b)
    mpfr_clear (b_copy);

}
