| /* mpfr_sub -- subtract two floating-point numbers |
| |
| Copyright 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. |
| Contributed by the Arenaire and Cacao 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 2.1 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.LIB. If not, write to |
| the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, |
| MA 02110-1301, USA. */ |
| |
| #include "mpfr-impl.h" |
| |
| int |
| mpfr_sub (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mp_rnd_t rnd_mode) |
| { |
| MPFR_LOG_FUNC (("b[%#R]=%R c[%#R]=%R rnd=%d", b, b, c, c, rnd_mode), |
| ("a[%#R]=%R", a, a)); |
| |
| if (MPFR_ARE_SINGULAR (b,c)) |
| { |
| if (MPFR_IS_NAN (b) || MPFR_IS_NAN (c)) |
| { |
| MPFR_SET_NAN (a); |
| MPFR_RET_NAN; |
| } |
| else if (MPFR_IS_INF (b)) |
| { |
| if (!MPFR_IS_INF (c) || MPFR_SIGN (b) != MPFR_SIGN(c)) |
| { |
| MPFR_SET_INF (a); |
| MPFR_SET_SAME_SIGN (a, b); |
| MPFR_RET (0); /* exact */ |
| } |
| else |
| { |
| MPFR_SET_NAN (a); /* Inf - Inf */ |
| MPFR_RET_NAN; |
| } |
| } |
| else if (MPFR_IS_INF (c)) |
| { |
| MPFR_SET_INF (a); |
| MPFR_SET_OPPOSITE_SIGN (a, c); |
| MPFR_RET (0); /* exact */ |
| } |
| else if (MPFR_IS_ZERO (b)) |
| { |
| if (MPFR_IS_ZERO (c)) |
| { |
| int sign = rnd_mode != GMP_RNDD |
| ? ((MPFR_IS_NEG(b) && MPFR_IS_POS(c)) ? -1 : 1) |
| : ((MPFR_IS_POS(b) && MPFR_IS_NEG(c)) ? 1 : -1); |
| MPFR_SET_SIGN (a, sign); |
| MPFR_SET_ZERO (a); |
| MPFR_RET(0); /* 0 - 0 is exact */ |
| } |
| else |
| return mpfr_neg (a, c, rnd_mode); |
| } |
| else |
| { |
| MPFR_ASSERTD (MPFR_IS_ZERO (c)); |
| return mpfr_set (a, b, rnd_mode); |
| } |
| } |
| MPFR_CLEAR_FLAGS (a); |
| MPFR_ASSERTD (MPFR_IS_PURE_FP (b) && MPFR_IS_PURE_FP (c)); |
| |
| if (MPFR_LIKELY (MPFR_SIGN (b) == MPFR_SIGN (c))) |
| { /* signs are equal, it's a real subtraction */ |
| if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b) |
| && MPFR_PREC (b) == MPFR_PREC (c))) |
| return mpfr_sub1sp (a, b, c, rnd_mode); |
| else |
| return mpfr_sub1 (a, b, c, rnd_mode); |
| } |
| else |
| { /* signs differ, it's an addition */ |
| if (MPFR_GET_EXP (b) < MPFR_GET_EXP (c)) |
| { /* exchange rounding modes towards +/- infinity */ |
| int inexact; |
| rnd_mode = MPFR_INVERT_RND (rnd_mode); |
| if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b) |
| && MPFR_PREC (b) == MPFR_PREC (c))) |
| inexact = mpfr_add1sp (a, c, b, rnd_mode); |
| else |
| inexact = mpfr_add1 (a, c, b, rnd_mode); |
| MPFR_CHANGE_SIGN (a); |
| return -inexact; |
| } |
| else |
| { |
| if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b) |
| && MPFR_PREC (b) == MPFR_PREC (c))) |
| return mpfr_add1sp (a, b, c, rnd_mode); |
| else |
| return mpfr_add1 (a, b, c, rnd_mode); |
| } |
| } |
| } |