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/* sys/ldfrexp.c
*
* Copyright (C) 2002, Gert Van den Eynde
* Copyright (C) 2007, Brian Gough
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or (at
* your option) any later version.
*
* This program 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <config.h>
#include <math.h>
#include <gsl/gsl_math.h>
double
gsl_ldexp (const double x, const int e)
{
int ex;
if (x == 0.0)
{
return x;
}
{
double y = gsl_frexp (x, &ex);
double e2 = e + ex, p2;
if (e2 >= DBL_MAX_EXP)
{
y *= pow (2.0, e2 - DBL_MAX_EXP + 1);
e2 = DBL_MAX_EXP - 1;
}
else if (e2 <= DBL_MIN_EXP)
{
y *= pow (2.0, e2 - DBL_MIN_EXP - 1);
e2 = DBL_MIN_EXP + 1;
}
p2 = pow (2.0, e2);
return y * p2;
}
}
double
gsl_frexp (const double x, int *e)
{
if (x == 0.0)
{
*e = 0;
return 0.0;
}
else if (!gsl_finite (x))
{
*e = 0;
return x;
}
else if (fabs (x) >= 0.5 && fabs (x) < 1) /* Handle the common case */
{
*e = 0;
return x;
}
else
{
double ex = ceil (log (fabs (x)) / M_LN2);
int ei = (int) ex;
double f;
/* Prevent underflow and overflow of 2**(-ei) */
if (ei < DBL_MIN_EXP)
ei = DBL_MIN_EXP;
if (ei > -DBL_MIN_EXP)
ei = -DBL_MIN_EXP;
f = x * pow (2.0, -ei);
if (!gsl_finite (f))
{
/* This should not happen */
*e = 0;
return f;
}
while (fabs (f) >= 1.0)
{
ei++;
f /= 2.0;
}
while (fabs (f) > 0 && fabs (f) < 0.5)
{
ei--;
f *= 2.0;
}
*e = ei;
return f;
}
}
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