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/* mpfr_get_float128 -- convert a multiple precision floating-point
number to a _Float128 number
Copyright 2012-2021 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"
#ifdef MPFR_WANT_FLOAT128
/* generic code */
_Float128
mpfr_get_float128 (mpfr_srcptr x, mpfr_rnd_t rnd_mode)
{
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
return (_Float128) mpfr_get_d (x, rnd_mode);
else /* now x is a normal non-zero number */
{
_Float128 r; /* result */
_Float128 m;
mpfr_exp_t e; /* exponent of x (before rounding) */
mpfr_exp_t sh; /* exponent shift, so that x/2^sh is in the double range */
const int emin = -16381;
const int esub = emin - IEEE_FLOAT128_MANT_DIG;
int sign;
sign = MPFR_SIGN (x);
e = MPFR_GET_EXP (x);
if (MPFR_UNLIKELY (e <= esub))
{
if (MPFR_IS_LIKE_RNDZ (rnd_mode, sign < 0) ||
(rnd_mode == MPFR_RNDN && (e < esub || mpfr_powerof2_raw (x))))
return sign < 0 ? -0.0 : 0.0;
r = 1.0;
sh = esub;
}
else
{
mpfr_t y;
mp_limb_t *yp;
int prec, i; /* small enough to fit in an int */
MPFR_SAVE_EXPO_DECL (expo);
MPFR_SAVE_EXPO_MARK (expo);
/* First round x to the target _Float128 precision, taking the
reduced precision of the subnormals into account, so that all
subsequent operations are exact (this avoids double rounding
problems). */
prec = e < emin ? e - esub : IEEE_FLOAT128_MANT_DIG;
MPFR_ASSERTD (prec >= MPFR_PREC_MIN);
mpfr_init2 (y, prec);
mpfr_set (y, x, rnd_mode);
sh = MPFR_GET_EXP (y);
MPFR_SET_EXP (y, 0);
MPFR_SET_POS (y);
yp = MPFR_MANT (y);
r = 0.0;
for (i = 0; i < MPFR_LIMB_SIZE (y); i++)
{
/* Note: MPFR_LIMB_MAX is avoided below as it might not
always work if GMP_NUMB_BITS > IEEE_FLOAT128_MANT_DIG.
MPFR_LIMB_HIGHBIT has the advantage to fit on 1 bit. */
r += yp[i];
r *= 1 / (2 * (_Float128) MPFR_LIMB_HIGHBIT);
}
mpfr_clear (y);
MPFR_SAVE_EXPO_FREE (expo);
}
/* we now have to multiply r by 2^sh */
MPFR_ASSERTD (r > 0);
if (sh != 0)
{
/* An overflow may occur (example: 0.5*2^1024) */
while (r < 1.0)
{
r += r;
sh--;
}
if (sh > 0)
m = 2.0;
else
{
m = 0.5;
sh = -sh;
}
for (;;)
{
if (sh % 2)
r = r * m;
sh >>= 1;
if (sh == 0)
break;
m = m * m;
}
}
if (sign < 0)
r = -r;
return r;
}
}
#endif /* MPFR_WANT_FLOAT128 */
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