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/* __gmp_extract_double -- convert from double to array of mp_limb_t.
Copyright (C) 1996 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
The GNU MP 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 Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#ifdef XDEBUG
#undef _GMP_IEEE_FLOATS
#endif
#ifndef _GMP_IEEE_FLOATS
#define _GMP_IEEE_FLOATS 0
#endif
/* Extract a non-negative double in d. */
int
#if __STDC__
__gmp_extract_double (mp_ptr rp, double d)
#else
__gmp_extract_double (rp, d)
mp_ptr rp;
double d;
#endif
{
long exp;
unsigned sc;
mp_limb_t manh, manl;
/* BUGS
1. Should handle Inf and NaN in IEEE specific code.
2. Handle Inf and NaN also in default code, to avoid hangs.
3. Generalize to handle all BITS_PER_MP_LIMB >= 32.
4. This lits is incomplete and misspelled.
*/
if (d == 0.0)
{
rp[0] = 0;
rp[1] = 0;
#if BITS_PER_MP_LIMB == 32
rp[2] = 0;
#endif
return 0;
}
#if _GMP_IEEE_FLOATS
{
union ieee_double_extract x;
x.d = d;
exp = x.s.exp;
#if BITS_PER_MP_LIMB == 64
manl = (((mp_limb_t) 1 << 63)
| ((mp_limb_t) x.s.manh << 43) | ((mp_limb_t) x.s.manl << 11));
if (exp == 0)
{
/* Denormalized number. Don't try to be clever about this,
since it is not an important case to make fast. */
exp = 1;
do
{
manl = manl << 1;
exp--;
}
while ((mp_limb_signed_t) manl >= 0);
}
#else
manh = ((mp_limb_t) 1 << 31) | (x.s.manh << 11) | (x.s.manl >> 21);
manl = x.s.manl << 11;
if (exp == 0)
{
/* Denormalized number. Don't try to be clever about this,
since it is not an important case to make fast. */
exp = 1;
do
{
manh = (manh << 1) | (manl >> 31);
manl = manl << 1;
exp--;
}
while ((mp_limb_signed_t) manh >= 0);
}
#endif
exp -= 1022; /* Remove IEEE bias. */
}
#else
{
/* Unknown (or known to be non-IEEE) double format. */
exp = 0;
if (d >= 1.0)
{
if (d * 0.5 == d)
abort ();
while (d >= 32768.0)
{
d *= (1.0 / 65536.0);
exp += 16;
}
while (d >= 1.0)
{
d *= 0.5;
exp += 1;
}
}
else if (d < 0.5)
{
while (d < (1.0 / 65536.0))
{
d *= 65536.0;
exp -= 16;
}
while (d < 0.5)
{
d *= 2.0;
exp -= 1;
}
}
d *= MP_BASE_AS_DOUBLE;
#if BITS_PER_MP_LIMB == 64
manl = d;
#else
manh = d;
manl = (d - manh) * MP_BASE_AS_DOUBLE;
#endif
}
#endif
sc = (unsigned) exp % BITS_PER_MP_LIMB;
/* We add something here to get rounding right. */
exp = (exp + 2048) / BITS_PER_MP_LIMB - 2048 / BITS_PER_MP_LIMB + 1;
#if BITS_PER_MP_LIMB == 64
if (sc != 0)
{
rp[1] = manl >> (BITS_PER_MP_LIMB - sc);
rp[0] = manl << sc;
}
else
{
rp[1] = manl;
rp[0] = 0;
exp--;
}
#else
if (sc != 0)
{
rp[2] = manh >> (BITS_PER_MP_LIMB - sc);
rp[1] = (manl >> (BITS_PER_MP_LIMB - sc)) | (manh << sc);
rp[0] = manl << sc;
}
else
{
rp[2] = manh;
rp[1] = manl;
rp[0] = 0;
exp--;
}
#endif
return exp;
}
|
