#include <stdio.h>
#include <math.h>
#include <values.h>
#include "opt.h"

#define	Debug		0
#define	Static		static

extern status IntervalReduction(dbl (*f)(), dbl a, dbl b, dbl *z, int timeout, dbl eps)
{
	int	k;
	dbl	ya, yb, xp, xm, xc, yc;
	
	ya = (*f)(a);
	yb = (*f)(b);
	
	if (fabs(ya) <= eps) {
		*z = a;
		return success;
	}
	if (fabs(yb) <= eps) {
		*z = b;
		return success;
	}
	
	if (ya > 0.00 && yb < 0.00) {
		xp = a;
		xm = b;
	} else if (ya < 0.00 && yb > 0.00) {
		xm = a;
		xp = b;
	} else {
		fprintf(stderr, "interval [ %lf  %lf ]\n", a, b);
		fprintf(stderr, "%lf and %lf have same sign\n", ya, yb);
		return failure;
	}
	
	for (k=0; k<timeout; k++) {
#if Debug
		fprintf(stderr, "interval [ %lf , %lf ]\n", xp, xm);
#endif
		xc = (xp + xm)/2.00;
		yc = (*f)(xc);
		if (fabs(yc) <= eps) {
			*z = xc;
			return success;
		}
		if (fabs(xp-xm) <= eps) {
			*z = xc;
			return success;
		}
		if (yc > 0.00) {
			xp = xc;
		} else {
			xm = xc;
		}
	}
	
	fprintf(stderr, "IntervalReduction timeout\n");
	return failure;
}