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/* mpfr_sub -- subtract two floating-point numbers
Copyright 2001, 2002, 2003 Free Software Foundation.
Contributed by the Spaces project, INRIA Lorraine.
This file is part of the MPFR Library.
The 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 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 MPFR Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#include "mpfr.h"
#include "mpfr-impl.h"
int
mpfr_sub (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mp_rnd_t rnd_mode)
{
if (MPFR_ARE_SINGULAR(b,c))
{
if (MPFR_IS_NAN(b) || MPFR_IS_NAN(c))
{
MPFR_SET_NAN(a);
MPFR_RET_NAN;
}
MPFR_CLEAR_NAN(a);
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);
MPFR_RET_NAN;
}
}
else
if (MPFR_IS_INF(c))
{
MPFR_SET_INF(a);
if (MPFR_SIGN(c) == MPFR_SIGN(a))
MPFR_CHANGE_SIGN(a);
MPFR_RET(0); /* exact */
}
if (MPFR_IS_ZERO(b))
{
if (MPFR_IS_ZERO(c))
{
if (MPFR_SIGN(a) !=
(rnd_mode != GMP_RNDD ?
((MPFR_SIGN(b) < 0 && MPFR_SIGN(c) > 0) ? -1 : 1) :
((MPFR_SIGN(b) > 0 && MPFR_SIGN(c) < 0) ? 1 : -1)))
MPFR_CHANGE_SIGN(a);
MPFR_CLEAR_INF(a);
MPFR_SET_ZERO(a);
MPFR_RET(0); /* 0 - 0 is exact */
}
return mpfr_neg (a, c, rnd_mode);
}
if (MPFR_IS_ZERO(c))
{
return mpfr_set (a, b, rnd_mode);
}
/* Should never reach here */
MPFR_ASSERTN(1);
}
MPFR_CLEAR_FLAGS(a);
MPFR_ASSERTD(MPFR_IS_PURE_FP(b) && MPFR_IS_PURE_FP(c));
if (MPFR_SIGN(b) == MPFR_SIGN(c))
{ /* signs are equal, it's a real subtraction */
return mpfr_sub1(a, b, c, rnd_mode, 1);
}
else
{ /* signs differ, it's an addition */
mp_exp_t eb, ec;
eb = MPFR_GET_EXP (b);
ec = MPFR_GET_EXP (c);
if (eb < ec)
{ /* exchange rounding modes towards +/- infinity */
int inexact;
if (rnd_mode == GMP_RNDU)
rnd_mode = GMP_RNDD;
else if (rnd_mode == GMP_RNDD)
rnd_mode = GMP_RNDU;
inexact = mpfr_add1(a, c, b, rnd_mode, (mp_exp_unsigned_t) ec - eb);
MPFR_CHANGE_SIGN(a);
return -inexact;
}
else
{
return mpfr_add1(a, b, c, rnd_mode, (mp_exp_unsigned_t) eb - ec);
}
}
}
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