/* 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;

    }

}