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/* mpfr_scale2 -- multiply a double float by 2^exp
Copyright 1999-2020 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 <float.h> /* for DBL_EPSILON */
#include "mpfr-impl.h"
/* Note: we could use the ldexp function, but since we want not to depend on
math.h, we write our own implementation. */
/* multiplies 1/2 <= d <= 1 by 2^exp */
double
mpfr_scale2 (double d, int exp)
{
#if _MPFR_IEEE_FLOATS
{
union mpfr_ieee_double_extract x;
if (MPFR_UNLIKELY (d == 1.0))
{
d = 0.5;
exp ++;
}
/* now 1/2 <= d < 1 */
/* infinities and zeroes have already been checked */
MPFR_ASSERTD (-1073 <= exp && exp <= 1025);
x.d = d;
if (MPFR_UNLIKELY (exp < -1021)) /* subnormal case */
{
x.s.exp += exp + 52;
x.d *= DBL_EPSILON;
}
else /* normalized case */
{
x.s.exp += exp;
}
return x.d;
}
#else /* _MPFR_IEEE_FLOATS */
{
double factor;
/* An overflow may occurs (example: 0.5*2^1024) */
if (d < 1.0)
{
d += d;
exp--;
}
/* Now 1.0 <= d < 2.0 */
if (exp < 0)
{
factor = 0.5;
exp = -exp;
}
else
{
factor = 2.0;
}
while (exp != 0)
{
if ((exp & 1) != 0)
d *= factor;
exp >>= 1;
factor *= factor;
}
return d;
}
#endif /* _MPFR_IEEE_FLOATS */
}
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