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/* 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 2 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));
}
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