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/* mpfr_get_ld -- convert a multiple precision floating-point number
to a machine long double
Copyright 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
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., 51 Franklin Place, Fifth Floor, Boston,
MA 02110-1301, USA. */
#include <float.h>
#include "mpfr-impl.h"
#ifndef HAVE_LDOUBLE_IEEE_EXT_LITTLE
long double
mpfr_get_ld (mpfr_srcptr x, mp_rnd_t rnd_mode)
{
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
return (long double) mpfr_get_d (x, rnd_mode);
else /* now x is a normal non-zero number */
{
long double r; /* result */
long double m;
double s; /* part of result */
mp_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 long double precision, so that
all subsequent operations are exact (this avoids double rounding
problems) */
mpfr_init2 (y, MPFR_LDBL_MANT_DIG);
mpfr_init2 (z, IEEE_DBL_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, GMP_RNDN); /* high part of y */
r += (long double) s;
mpfr_set_d (z, s, GMP_RNDN); /* exact */
mpfr_sub (y, y, z, GMP_RNDN); /* exact */
} while (!MPFR_IS_ZERO (y));
mpfr_clear (z);
mpfr_clear (y);
/* we now have to multiply back by 2^sh */
MPFR_ASSERTD (r > 0);
if (sh != 0)
{
/* An overflow may occurs (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;
}
}
#else
static const struct {
char bytes[10];
long double dummy; /* for memory alignment */
} ldbl_max_struct = {
{ '\377','\377','\377','\377',
'\377','\377','\377','\377',
'\376','\177' }, 0.0
};
#define MPFR_LDBL_MAX (* (const long double *) ldbl_max_struct.bytes)
long double
mpfr_get_ld (mpfr_srcptr x, mp_rnd_t rnd_mode)
{
mpfr_long_double_t ld;
mpfr_t tmp;
MPFR_SAVE_EXPO_DECL (expo);
MPFR_SAVE_EXPO_MARK (expo);
mpfr_set_emin (-16382-63);
mpfr_set_emax (16383);
mpfr_init2 (tmp, MPFR_LDBL_MANT_DIG);
mpfr_subnormalize(tmp, mpfr_set (tmp, x, rnd_mode), rnd_mode);
mpfr_prec_round (tmp, 64, GMP_RNDZ); /* exact */
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (tmp)))
ld.ld = (long double) mpfr_get_d (tmp, rnd_mode);
else
{
mp_limb_t *tmpmant;
mp_exp_t e, denorm;
tmpmant = MPFR_MANT (tmp);
e = MPFR_GET_EXP (tmp);
denorm = MPFR_UNLIKELY (e < -16382) ? - e - 16382 + 1 : 0;
#if BITS_PER_MP_LIMB >= 64
ld.s.manl = (tmpmant[0] >> denorm);
ld.s.manh = (tmpmant[0] >> denorm) >> 32;
#elif BITS_PER_MP_LIMB == 32
if (MPFR_LIKELY (denorm == 0))
{
ld.s.manl = tmpmant[0];
ld.s.manh = tmpmant[1];
}
else if (denorm < 32)
{
ld.s.manl = (tmpmant[0] >> denorm) | (tmpmant[1] << (32 - denorm));
ld.s.manh = tmpmant[1] >> denorm;
}
else /* 32 <= denorm <= 64 */
{
ld.s.manl = tmpmant[1] >> (denorm - 32);
ld.s.manh = 0;
}
#else
# error "BITS_PER_MP_LIMB must be 32 or >= 64"
/* Other values have never been supported anyway. */
#endif
if (MPFR_LIKELY (denorm == 0))
{
ld.s.exph = (e + 0x3FFE) >> 8;
ld.s.expl = (e + 0x3FFE);
}
else
ld.s.exph = ld.s.expl = 0;
ld.s.sign = MPFR_IS_NEG (x);
}
mpfr_clear (tmp);
MPFR_SAVE_EXPO_FREE (expo);
return ld.ld;
}
#endif
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