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Diffstat (limited to 'src/sub.c')
| -rw-r--r-- | src/sub.c | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/src/sub.c b/src/sub.c new file mode 100644 index 0000000..d1af16f --- /dev/null +++ b/src/sub.c @@ -0,0 +1,116 @@ +/* mpfr_sub -- subtract two floating-point numbers + +Copyright 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc. +Contributed by the AriC and Caramel 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 3 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.LESSER. If not, see +http://www.gnu.org/licenses/ or 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, mpfr_rnd_t rnd_mode) +{ + MPFR_LOG_FUNC + (("b[%Pu]=%.*Rg c[%Pu]=%.*Rg rnd=%d", + mpfr_get_prec (b), mpfr_log_prec, b, + mpfr_get_prec (c), mpfr_log_prec, c, rnd_mode), + ("a[%Pu]=%.*Rg", mpfr_get_prec (a), mpfr_log_prec, 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 != MPFR_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_ASSERTD (MPFR_IS_PURE_FP (b)); + MPFR_ASSERTD (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 toward +/- 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); + } + } +} |