source: sasmodels/sasmodels/models/lib/polevl.c @ 0b05c24

/*                                                      polevl.c
 *                                                      p1evl.c
 *
 *      Evaluate polynomial
 *
 *
 *
 * SYNOPSIS:
 *
 * 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, constant double *coef, int N ) {

    int i = 0;
    double ans = coef[i];

    while (i < N) {
        i++;
        ans = ans * x + coef[i];
    }

    return ans ;
}

/*                                                      p1evl() */
/*                                          N
 * Evaluate polynomial when coefficient of x  is 1.0.
 * Otherwise same as polevl.
 */

double p1evl( double x, constant double *coef, int N ) {
    int i=0;
    double ans = x+coef[i];

    while (i < N-1) {
        i++;
        ans = ans*x + coef[i];
    }

    return( ans );
}