/*	
	Title: Test function sf(x)

	This will test the function 'sf' given in Section 3 of
	Chapter 1.  When the program is running, let the input variable
	x equal 0 to stop.
*/

#include <stdio.h>

float sf(float x);

main()
{
	float x;   
 
	while (1) {
		printf("\n\tWhat is x?  Give  0  to stop : ");
		scanf("%f", &x);
		if (x == 0.0)
			return(0);
		printf("\n\t x = %f \t sf(x) = %f\n", x, sf(x));
	}
}


float sf(float x)
{ 

/*	
	This evaluates an approximation to
 
            		1         x  1
    		sf(x) = - integral   - sin(t)*dt
            		x         0  t
 
	For -1 <= x <= 1, the approximation is the
	degree 8 Taylor polynomial for sf(x).  Its
	maximum error is 5.0e-9, provided the computer
	arithmetic allows a relative error of that size.
*/

	
	float u, value, a[5] = { 1.0, -1.0/18.0, 1.0/600.0, 
							-1.0/35280.0, 1.0/3265920.0 };
	int ndeg = 4, i;
 	

	/* Initialize */
 
	u = x*x;		
	value = a[ndeg];

	/* Do nested multiplication */
 
	for (i = ndeg; i >= 0; i--)	
		value = a[i] + u*value;

	return(value);
}