1 /* mpfr_sub -- subtract two floating-point numbers
2
3 Copyright 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
4 Contributed by the AriC and Caramel projects, INRIA.
5
6 This file is part of the GNU MPFR Library.
7
8 The GNU MPFR Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or (at your
11 option) any later version.
12
13 The GNU MPFR Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
17
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22
23 #include "mpfr-impl.h"
24
25 int
mpfr_sub(mpfr_ptr a,mpfr_srcptr b,mpfr_srcptr c,mpfr_rnd_t rnd_mode)26 mpfr_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