contrib/mpfr/sub.c

   1 /* mpfr_sub -- subtract two floating-point numbers
   2
   3 Copyright 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
   4 Contributed by the Arenaire and Cacao 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 2.1 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.LIB.  If not, write to
  20 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  21 MA 02110-1301, USA. */
  22
  23 #include "mpfr-impl.h"
  24
  25 int
  26 mpfr_sub (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mp_rnd_t rnd_mode)
  27 {
  28   MPFR_LOG_FUNC (("b[%#R]=%R c[%#R]=%R rnd=%d", b, b, c, c, rnd_mode),
  29                  ("a[%#R]=%R", a, a));
  30
  31   if (MPFR_ARE_SINGULAR (b,c))
  32     {
  33       if (MPFR_IS_NAN (b) || MPFR_IS_NAN (c))
  34         {
  35           MPFR_SET_NAN (a);
  36           MPFR_RET_NAN;
  37         }
  38       else if (MPFR_IS_INF (b))
  39         {
  40           if (!MPFR_IS_INF (c) || MPFR_SIGN (b) != MPFR_SIGN(c))
  41             {
  42               MPFR_SET_INF (a);
  43               MPFR_SET_SAME_SIGN (a, b);
  44               MPFR_RET (0); /* exact */
  45             }
  46           else
  47             {
  48               MPFR_SET_NAN (a); /* Inf - Inf */
  49               MPFR_RET_NAN;
  50             }
  51         }
  52       else if (MPFR_IS_INF (c))
  53         {
  54           MPFR_SET_INF (a);
  55           MPFR_SET_OPPOSITE_SIGN (a, c);
  56           MPFR_RET (0); /* exact */
  57         }
  58       else if (MPFR_IS_ZERO (b))
  59         {
  60           if (MPFR_IS_ZERO (c))
  61             {
  62               int sign = rnd_mode != GMP_RNDD
  63                 ? ((MPFR_IS_NEG(b) && MPFR_IS_POS(c)) ? -1 : 1)
  64                 : ((MPFR_IS_POS(b) && MPFR_IS_NEG(c)) ? 1 : -1);
  65               MPFR_SET_SIGN (a, sign);
  66               MPFR_SET_ZERO (a);
  67               MPFR_RET(0); /* 0 - 0 is exact */
  68             }
  69           else
  70             return mpfr_neg (a, c, rnd_mode);
  71         }
  72       else
  73         {
  74           MPFR_ASSERTD (MPFR_IS_ZERO (c));
  75           return mpfr_set (a, b, rnd_mode);
  76         }
  77     }
  78   MPFR_CLEAR_FLAGS (a);
  79   MPFR_ASSERTD (MPFR_IS_PURE_FP (b) && MPFR_IS_PURE_FP (c));
  80
  81   if (MPFR_LIKELY (MPFR_SIGN (b) == MPFR_SIGN (c)))
  82     { /* signs are equal, it's a real subtraction */
  83       if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b)
  84                        && MPFR_PREC (b) == MPFR_PREC (c)))
  85         return mpfr_sub1sp (a, b, c, rnd_mode);
  86       else
  87         return mpfr_sub1 (a, b, c, rnd_mode);
  88     }
  89   else
  90     { /* signs differ, it's an addition */
  91       if (MPFR_GET_EXP (b) < MPFR_GET_EXP (c))
  92          { /* exchange rounding modes towards +/- infinity */
  93           int inexact;
  94           rnd_mode = MPFR_INVERT_RND (rnd_mode);
  95           if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b)
  96                            && MPFR_PREC (b) == MPFR_PREC (c)))
  97             inexact = mpfr_add1sp (a, c, b, rnd_mode);
  98           else
  99             inexact = mpfr_add1 (a, c, b, rnd_mode);
 100           MPFR_CHANGE_SIGN (a);
 101           return -inexact;
 102         }
 103       else
 104         {
 105           if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b)
 106                            && MPFR_PREC (b) == MPFR_PREC (c)))
 107             return mpfr_add1sp (a, b, c, rnd_mode);
 108           else
 109             return mpfr_add1 (a, b, c, rnd_mode);
 110         }
 111     }
 112 }