1 /* mpfr_sub -- subtract two floating-point numbers
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.
6 This file is part of the GNU MPFR Library.
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.
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.
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. */
23 #include "mpfr-impl.h"
26 mpfr_sub (mpfr_ptr a
, mpfr_srcptr b
, mpfr_srcptr c
, mpfr_rnd_t rnd_mode
)
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
));
34 if (MPFR_ARE_SINGULAR (b
,c
))
36 if (MPFR_IS_NAN (b
) || MPFR_IS_NAN (c
))
41 else if (MPFR_IS_INF (b
))
43 if (!MPFR_IS_INF (c
) || MPFR_SIGN (b
) != MPFR_SIGN(c
))
46 MPFR_SET_SAME_SIGN (a
, b
);
47 MPFR_RET (0); /* exact */
51 MPFR_SET_NAN (a
); /* Inf - Inf */
55 else if (MPFR_IS_INF (c
))
58 MPFR_SET_OPPOSITE_SIGN (a
, c
);
59 MPFR_RET (0); /* exact */
61 else if (MPFR_IS_ZERO (b
))
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
);
70 MPFR_RET(0); /* 0 - 0 is exact */
73 return mpfr_neg (a
, c
, rnd_mode
);
77 MPFR_ASSERTD (MPFR_IS_ZERO (c
));
78 return mpfr_set (a
, b
, rnd_mode
);
82 MPFR_ASSERTD (MPFR_IS_PURE_FP (b
));
83 MPFR_ASSERTD (MPFR_IS_PURE_FP (c
));
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
);
91 return mpfr_sub1 (a
, b
, c
, rnd_mode
);
94 { /* signs differ, it's an addition */
95 if (MPFR_GET_EXP (b
) < MPFR_GET_EXP (c
))
96 { /* exchange rounding modes toward +/- infinity */
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
);
103 inexact
= mpfr_add1 (a
, c
, b
, rnd_mode
);
104 MPFR_CHANGE_SIGN (a
);
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
);
113 return mpfr_add1 (a
, b
, c
, rnd_mode
);