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/* mpfr_sub -- subtract two floating-point numbers
Copyright 2001-2004, 2006-2021 Free Software Foundation, Inc.
Contributed by the AriC and Caramba 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
https://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"
MPFR_HOT_FUNCTION_ATTR 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_OR_UBF (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 if (MPFR_IS_ZERO (c))
{
return mpfr_set (a, b, rnd_mode);
}
else
{
MPFR_ASSERTD (MPFR_IS_PURE_UBF (b));
MPFR_ASSERTD (MPFR_IS_PURE_UBF (c));
/* mpfr_sub1sp and mpfr_add1sp are not intended to support UBF,
for which optimization is less important. */
if (MPFR_SIGN(b) == MPFR_SIGN(c))
return mpfr_sub1 (a, b, c, rnd_mode);
else if (MPFR_UBF_EXP_LESS_P (b, c))
{
int inexact;
rnd_mode = MPFR_INVERT_RND (rnd_mode);
inexact = mpfr_add1 (a, c, b, rnd_mode);
MPFR_CHANGE_SIGN (a);
return -inexact;
}
else
return mpfr_add1 (a, b, c, 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);
}
}
}
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