1/* mpfr_sub -- subtract two floating-point numbers
2
3Copyright 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
4Contributed by the AriC and Caramel 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
25int
26mpfr_sub (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode)
27{
28  MPFR_LOG_FUNC
29    (("b[%Pu]=%.*Rg c[%Pu]=%.*Rg rnd=%d",
30      mpfr_get_prec (b), mpfr_log_prec, b,
31      mpfr_get_prec (c), mpfr_log_prec, c, rnd_mode),
32     ("a[%Pu]=%.*Rg", mpfr_get_prec (a), mpfr_log_prec, a));
33
34  if (MPFR_ARE_SINGULAR (b,c))
35    {
36      if (MPFR_IS_NAN (b) || MPFR_IS_NAN (c))
37        {
38          MPFR_SET_NAN (a);
39          MPFR_RET_NAN;
40        }
41      else if (MPFR_IS_INF (b))
42        {
43          if (!MPFR_IS_INF (c) || MPFR_SIGN (b) != MPFR_SIGN(c))
44            {
45              MPFR_SET_INF (a);
46              MPFR_SET_SAME_SIGN (a, b);
47              MPFR_RET (0); /* exact */
48            }
49          else
50            {
51              MPFR_SET_NAN (a); /* Inf - Inf */
52              MPFR_RET_NAN;
53            }
54        }
55      else if (MPFR_IS_INF (c))
56        {
57          MPFR_SET_INF (a);
58          MPFR_SET_OPPOSITE_SIGN (a, c);
59          MPFR_RET (0); /* exact */
60        }
61      else if (MPFR_IS_ZERO (b))
62        {
63          if (MPFR_IS_ZERO (c))
64            {
65              int sign = rnd_mode != MPFR_RNDD
66                ? ((MPFR_IS_NEG(b) && MPFR_IS_POS(c)) ? -1 : 1)
67                : ((MPFR_IS_POS(b) && MPFR_IS_NEG(c)) ? 1 : -1);
68              MPFR_SET_SIGN (a, sign);
69              MPFR_SET_ZERO (a);
70              MPFR_RET(0); /* 0 - 0 is exact */
71            }
72          else
73            return mpfr_neg (a, c, rnd_mode);
74        }
75      else
76        {
77          MPFR_ASSERTD (MPFR_IS_ZERO (c));
78          return mpfr_set (a, b, rnd_mode);
79        }
80    }
81
82  MPFR_ASSERTD (MPFR_IS_PURE_FP (b));
83  MPFR_ASSERTD (MPFR_IS_PURE_FP (c));
84
85  if (MPFR_LIKELY (MPFR_SIGN (b) == MPFR_SIGN (c)))
86    { /* signs are equal, it's a real subtraction */
87      if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b)
88                       && MPFR_PREC (b) == MPFR_PREC (c)))
89        return mpfr_sub1sp (a, b, c, rnd_mode);
90      else
91        return mpfr_sub1 (a, b, c, rnd_mode);
92    }
93  else
94    { /* signs differ, it's an addition */
95      if (MPFR_GET_EXP (b) < MPFR_GET_EXP (c))
96         { /* exchange rounding modes toward +/- infinity */
97          int inexact;
98          rnd_mode = MPFR_INVERT_RND (rnd_mode);
99          if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b)
100                           && MPFR_PREC (b) == MPFR_PREC (c)))
101            inexact = mpfr_add1sp (a, c, b, rnd_mode);
102          else
103            inexact = mpfr_add1 (a, c, b, rnd_mode);
104          MPFR_CHANGE_SIGN (a);
105          return -inexact;
106        }
107      else
108        {
109          if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b)
110                           && MPFR_PREC (b) == MPFR_PREC (c)))
111            return mpfr_add1sp (a, b, c, rnd_mode);
112          else
113            return mpfr_add1 (a, b, c, rnd_mode);
114        }
115    }
116}
117