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/* mpfr_get_float128 -- convert a multiple precision floating-point
number to a __float128 number
Copyright 2012, 2013 Free Software Foundation, Inc.
Contributed by the AriC and Caramel 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
http://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;
double s; /* part of result */
mpfr_exp_t sh; /* exponent shift, so that x/2^sh is in the double range */
mpfr_t y, z;
int sign;
/* first round x to the target __float128 precision, so that
all subsequent operations are exact (this avoids double rounding
problems) */
mpfr_init2 (y, IEEE_FLOAT128_MANT_DIG);
mpfr_init2 (z, IEEE_FLOAT128_MANT_DIG);
mpfr_set (y, x, rnd_mode);
sh = MPFR_GET_EXP (y);
sign = MPFR_SIGN (y);
MPFR_SET_EXP (y, 0);
MPFR_SET_POS (y);
r = 0.0;
do
{
s = mpfr_get_d (y, MPFR_RNDN); /* high part of y */
r += (__float128) s;
mpfr_set_d (z, s, MPFR_RNDN); /* exact */
mpfr_sub (y, y, z, MPFR_RNDN); /* exact */
}
while (MPFR_NOTZERO (y));
mpfr_clear (z);
mpfr_clear (y);
/* 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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