source/libs/mpfr/mpfr-3.1.3/src/sub.c

   1 /* mpfr_sub -- subtract two floating-point numbers
   2
   3 Copyright 2001-2004, 2006-2015 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
  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 }