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polevl.c

/*                                        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, 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;
}

/* 
 * 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;
}

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