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/* specfunc/elementary.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_elementary.h>
#include "error.h"
#include "check.h"
int
gsl_sf_multiply_e(const double x, const double y, gsl_sf_result * result)
{
const double ax = fabs(x);
const double ay = fabs(y);
if(x == 0.0 || y == 0.0) {
/* It is necessary to eliminate this immediately.
*/
result->val = 0.0;
result->err = 0.0;
return GSL_SUCCESS;
}
else if((ax <= 1.0 && ay >= 1.0) || (ay <= 1.0 && ax >= 1.0)) {
/* Straddling 1.0 is always safe.
*/
result->val = x*y;
result->err = 2.0 * GSL_DBL_EPSILON * fabs(result->val);
return GSL_SUCCESS;
}
else {
const double f = 1.0 - 2.0 * GSL_DBL_EPSILON;
const double min = GSL_MIN_DBL(fabs(x), fabs(y));
const double max = GSL_MAX_DBL(fabs(x), fabs(y));
if(max < 0.9 * GSL_SQRT_DBL_MAX || min < (f * DBL_MAX)/max) {
result->val = GSL_COERCE_DBL(x*y);
result->err = 2.0 * GSL_DBL_EPSILON * fabs(result->val);
CHECK_UNDERFLOW(result);
return GSL_SUCCESS;
}
else {
OVERFLOW_ERROR(result);
}
}
}
int
gsl_sf_multiply_err_e(const double x, const double dx,
const double y, const double dy,
gsl_sf_result * result)
{
int status = gsl_sf_multiply_e(x, y, result);
result->err += fabs(dx*y) + fabs(dy*x);
return status;
}
/*-*-*-*-*-*-*-*-*-* Functions w/ Natural Prototypes *-*-*-*-*-*-*-*-*-*-*/
#include "eval.h"
double gsl_sf_multiply(const double x, const double y)
{
EVAL_RESULT(gsl_sf_multiply_e(x, y, &result));
}
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