/* sys/expm1.c

 * 

 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Gerard Jungman, 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_expm1 (const double x)

{

  /* FIXME: this should be improved */

  if (fabs(x) < M_LN2)

    {

      /* Compute the taylor series S = x + (1/2!) x^2 + (1/3!) x^3 + ... */

      double i = 1.0;

      double sum = x;

      double term = x / 1.0;

      do

        {

          i++ ;

          term *= x/i;

          sum += term;

        }

      while (fabs(term) > fabs(sum) * GSL_DBL_EPSILON) ;

      return sum ;

    }

  else

    {

      return exp(x) - 1;

    }

}