#include <math.h>

#define JMAX 40

float rtbis(func,x1,x2,xacc)
float x1,x2,xacc;
float (*func)();	/* ANSI: float (*func)(float); */
{
	int j;
	float dx,f,fmid,xmid,rtb;
	void nrerror();

	f=(*func)(x1);
	fmid=(*func)(x2);
	if (f*fmid >= 0.0) nrerror("Root must be bracketed for bisection in RTBIS");
	rtb = f < 0.0 ? (dx=x2-x1,x1) : (dx=x1-x2,x2);
	for (j=1;j<=JMAX;j++) {
		fmid=(*func)(xmid=rtb+(dx *= 0.5));
		if (fmid <= 0.0) rtb=xmid;
		if (fabs(dx) < xacc || fmid == 0.0) return rtb;
	}
	nrerror("Too many bisections in RTBIS");
}

#undef JMAX