text: /* specfunc/pow_int.c
   * 
   * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
   * 
   * 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.
   */
  
  /* Author:  G. Jungman */
  
  #include <config.h>
  #include <gsl/gsl_math.h>
  #include <gsl/gsl_errno.h>
  #include <gsl/gsl_sf_pow_int.h>
  
  
  /*-*-*-*-*-*-*-*-*-*-*-* Functions w/ Error handling *-*-*-*-*-*-*-*-*-*-*-*/
  
  int gsl_sf_pow_int_e(double x, int n, gsl_sf_result * result)
  {
    double value = 1.0;
    int count = 0;
  
    /* CHECK_POINTER(result) */
  
  
    if(n < 0) {
      n = -n;
  
      if(x == 0.0) {
        double u = 1.0 / x;
        result->val = (n % 2) ? u : (u * u) ;  /* correct sign of infinity */
        result->err = GSL_POSINF;
        GSL_ERROR ("overflow", GSL_EOVRFLW);
      }
  
      x = 1.0/x;
    }
  
    /* repeated squaring method 
     * returns 0.0^0 = 1.0, so continuous in x
     */
    do {
       if(GSL_IS_ODD(n)) value *= x;
       n >>= 1;
       x *= x;
       ++count;
    } while (n);
  
    result->val = value;
    result->err = 2.0 * GSL_DBL_EPSILON * (count + 1.0) * fabs(value); 
  
    return GSL_SUCCESS;
  }
  
  /*-*-*-*-*-*-*-*-*-* Functions w/ Natural Prototypes *-*-*-*-*-*-*-*-*-*-*/
  
  #include "eval.h"
  
  double gsl_sf_pow_int(const double x, const int n)
  {
    EVAL_RESULT(gsl_sf_pow_int_e(x, n, &result));
  }
  