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/* mpfr_get_ld, mpfr_get_ld_2exp -- convert a multiple precision floating-point
number to a machine long double
Copyright 2002-2016 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
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, 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, mpfr_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 */
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 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, MPFR_LDBL_MANT_DIG);
/* Note about the precision of z: even though IEEE_DBL_MANT_DIG is
sufficient, z has been set to the same precision as y so that
the mpfr_sub below calls mpfr_sub1sp, which is faster than the
generic subtraction, even in this particular case (from tests
done by Patrick Pelissier on a 64-bit Core2 Duo against r7285).
But here there is an important cancellation in the subtraction.
TODO: get more information about what has been tested. */
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 += (long double) s;
mpfr_set_d (z, s, MPFR_RNDN); /* exact */
mpfr_sub (y, y, z, MPFR_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
long double
mpfr_get_ld (mpfr_srcptr x, mpfr_rnd_t rnd_mode)
{
mpfr_long_double_t ld;
mpfr_t tmp;
int inex;
MPFR_SAVE_EXPO_DECL (expo);
MPFR_SAVE_EXPO_MARK (expo);
mpfr_init2 (tmp, MPFR_LDBL_MANT_DIG);
inex = mpfr_set (tmp, x, rnd_mode);
mpfr_set_emin (-16381-63); /* emin=-16444 */
mpfr_set_emax (16384);
mpfr_subnormalize (tmp, mpfr_check_range (tmp, inex, rnd_mode), rnd_mode);
mpfr_prec_round (tmp, 64, MPFR_RNDZ); /* exact */
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (tmp)))
ld.ld = (long double) mpfr_get_d (tmp, rnd_mode);
else
{
mp_limb_t *tmpmant;
mpfr_exp_t e, denorm;
tmpmant = MPFR_MANT (tmp);
e = MPFR_GET_EXP (tmp);
/* the smallest normal number is 2^(-16382), which is 0.5*2^(-16381)
in MPFR, thus any exponent <= -16382 corresponds to a subnormal
number */
denorm = MPFR_UNLIKELY (e <= -16382) ? - e - 16382 + 1 : 0;
#if GMP_NUMB_BITS >= 64
ld.s.manl = (tmpmant[0] >> denorm);
ld.s.manh = (tmpmant[0] >> denorm) >> 32;
#elif GMP_NUMB_BITS == 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 "GMP_NUMB_BITS 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
/* contributed by Damien Stehle */
long double
mpfr_get_ld_2exp (long *expptr, mpfr_srcptr src, mpfr_rnd_t rnd_mode)
{
long double ret;
mpfr_exp_t exp;
mpfr_t tmp;
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (src)))
return (long double) mpfr_get_d_2exp (expptr, src, rnd_mode);
tmp[0] = *src; /* Hack copy mpfr_t */
MPFR_SET_EXP (tmp, 0);
ret = mpfr_get_ld (tmp, rnd_mode);
if (MPFR_IS_PURE_FP(src))
{
exp = MPFR_GET_EXP (src);
/* rounding can give 1.0, adjust back to 0.5 <= abs(ret) < 1.0 */
if (ret == 1.0)
{
ret = 0.5;
exp ++;
}
else if (ret == -1.0)
{
ret = -0.5;
exp ++;
}
MPFR_ASSERTN ((ret >= 0.5 && ret < 1.0)
|| (ret <= -0.5 && ret > -1.0));
MPFR_ASSERTN (exp >= LONG_MIN && exp <= LONG_MAX);
}
else
exp = 0;
*expptr = exp;
return ret;
}
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