reldiff.c revision 1.1.1.1 
1/* mpfr_reldiff -- compute relative difference of two floating-point numbers.
2
3Copyright 2000, 2001, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
4Contributed by the Arenaire and Cacao projects, INRIA.
5
6This file is part of the GNU MPFR Library.
7
8The GNU MPFR Library is free software; you can redistribute it and/or modify
9it under the terms of the GNU Lesser General Public License as published by
10the Free Software Foundation; either version 3 of the License, or (at your
11option) any later version.
12
13The GNU MPFR Library is distributed in the hope that it will be useful, but
14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16License for more details.
17
18You should have received a copy of the GNU Lesser General Public License
19along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
20http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
2151 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22
23#include "mpfr-impl.h"
24
25/* reldiff(b, c) = abs(b-c)/b */
26void
27mpfr_reldiff (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode)
28{
29  mpfr_t b_copy;
30
31  if (MPFR_ARE_SINGULAR (b, c))
32    {
33      if (MPFR_IS_NAN(b) || MPFR_IS_NAN(c))
34        {
35          MPFR_SET_NAN(a);
36          return;
37        }
38      else if (MPFR_IS_INF(b))
39        {
40          if (MPFR_IS_INF (c) && (MPFR_SIGN (c) == MPFR_SIGN (b)))
41            MPFR_SET_ZERO(a);
42          else
43            MPFR_SET_NAN(a);
44          return;
45        }
46      else if (MPFR_IS_INF(c))
47        {
48          MPFR_SET_SAME_SIGN (a, b);
49          MPFR_SET_INF (a);
50          return;
51        }
52      else if (MPFR_IS_ZERO(b)) /* reldiff = abs(c)/c = sign(c) */
53        {
54          mpfr_set_si (a, MPFR_INT_SIGN (c), rnd_mode);
55          return;
56        }
57      /* Fall through */
58    }
59
60  if (a == b)
61    {
62      mpfr_init2 (b_copy, MPFR_PREC(b));
63      mpfr_set (b_copy, b, MPFR_RNDN);
64    }
65
66  mpfr_sub (a, b, c, rnd_mode);
67  mpfr_abs (a, a, rnd_mode); /* for compatibility with MPF */
68  mpfr_div (a, a, (a == b) ? b_copy : b, rnd_mode);
69
70  if (a == b)
71    mpfr_clear (b_copy);
72
73}
74