polevl.cpp

math software

//
// polevl.cpp
//
// polevl.cpp,v 1.3 2003/01/15 09:08:21 tonyottosson Exp
//


#include "../src/base/bessel/bessel_internal.h"

// This is slightly modified routine from the Cephes library, see http://www.netlib.org/cephes/
//  
// According to licence agreement this software can be used freely.
//

/*
 *	Evaluate polynomial
 *
 * int N;
 * double x, y, coef[N+1], polevl[];
 *
 * y = polevl( x, coef, N );
 *
 * DESCRIPTION:
 *
 * Evaluates polynomial of degree N:
 *
 *                     2          N
 * y  =  C  + C x + C x  +...+ C x
 *        0    1     2          N
 *
 * Coefficients are stored in reverse order:
 *
 * coef[0] = C  , ..., coef[N] = C  .
 *            N                   0
 *
 *  The function p1evl() assumes that coef[N] = 1.0 and is
 * omitted from the array.  Its calling arguments are
 * otherwise the same as polevl().
 *
 * SPEED:
 *
 * In the interest of speed, there are no checks for out
 * of bounds arithmetic.  This routine is used by most of
 * the functions in the library.  Depending on available
 * equipment features, the user may wish to rewrite the
 * program in microcode or assembly language.
 */


/*
Cephes Math Library Release 2.1:  December, 1988
Copyright 1984, 1987, 1988 by Stephen L. Moshier
Direct inquiries to 30 Frost Street, Cambridge, MA 02140
*/

double polevl(double x, double coef[], int N)
{
  double ans;
  int i;
  double *p;

  p = coef;
  ans = *p++;
  i = N;

  do
    ans = ans * x  +  *p++;
  while( --i );

  return( ans );
}

/*                                          N
 * Evaluate polynomial when coefficient of x  is 1.0.
 * Otherwise same as polevl.
 */

double p1evl(double x, double coef[], int N)
{
  double ans;
  double *p;
  int i;

  p = coef;
  ans = x + *p++;
  i = N-1;

  do
    ans = ans * x  + *p++;
  while( --i );

  return( ans );
}