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/* mpfr_sub -- subtract two floating-point numbers
Copyright 2001, 2002, 2003, 2004 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 "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;
}
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);
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 */
}
else if (MPFR_IS_ZERO(b))
{
if (MPFR_IS_ZERO(c))
{
if (MPFR_SIGN(a) !=
(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_CHANGE_SIGN(a);
MPFR_SET_ZERO(a);
MPFR_RET(0); /* 0 - 0 is exact */
}
return mpfr_neg (a, c, rnd_mode);
}
else if (MPFR_IS_ZERO(c))
{
return mpfr_set (a, b, rnd_mode);
}
/* Should never reach here */
MPFR_ASSERTN(0);
}
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;
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);
MPFR_CHANGE_SIGN(a);
return -inexact;
}
else
{
return mpfr_add1(a, b, c, rnd_mode);
}
}
}
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