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bool mengerSponge(double x, double y, double z) {

	if(x<0 || x>1 || y<0 || y>1 || z<0 || z>1 )     { return 0; } 		// point is not part of menger sponge

	int iterations=8;

	double depth=3;

	for(int iter=0; iter<iterations; iter++) {
		int holex=1;
		while(holex<depth) {
			int holey=1;
			while(holey<depth) {
				if(
					 ((x > holex/depth && x< (holex+1) /depth) && (y > holey/depth && y< (holey+1) /depth)) ||
					 ((y > holex/depth && y< (holex+1) /depth) && (z > holey/depth && z< (holey+1) /depth)) ||
					 ((x > holex/depth && x< (holex+1) /depth) && (z > holey/depth && z< (holey+1) /depth))
					 ) { return 0; }		// point is not part of menger sponge
				holey+=3;
			}
			holex+=3;
		}
		depth*=3;
	}

	return 1;	// point is part of menger sponge
}

bool MengerSponge(double x, double y, double z) {
	int iterations=7;
	if(x<0.0 || x>1 || y<0 || y>1 || z<0 || z>1 )     { return 0; } // Not part of menger sponge
	double p=3.0;
	for(int m=1; m<iterations; m++) {
		double xa = floatmod(x*p, 3);
		double ya = floatmod(y*p, 3);
		double za = floatmod(z*p, 3);
		if(
			(xa > 1.0 && xa < 2.0   &&   ya > 1.0 && ya < 2.0) ||
			(ya > 1.0 && ya < 2.0   &&   za > 1.0 && za < 2.0) ||
			(xa > 1.0 && xa < 2.0   &&   za > 1.0 && za < 2.0)

			) {return 0;}  // Not part of menger sponge
		p*=3;
	}
	return 1;  // Is part of menger sponge
}

for (L = 0; L < N; L++)
{
  double xx = fmod(a * k, 2.0)-1.0;
  double yy = fmod(b * k, 2.0)-1.0;
  double zz = fmod(c * k, 2.0)-1.0;
  if ((xx*xx + yy*yy + zz*zz < 1.03))
  {
     result = 0;
     break;
   }
   k *= 4.0;
   result = 1;
}

//Derived from twinbee's algorithm
MengerSponge3(x, y, z) {//by recursively digging a box
   x=x*0.5+0.5;y=y*0.5+0.5;z=z*0.5+0.5;//center it by changing position and scale
   
   xx=abs(x-0.5)-0.5;yy=abs(y-0.5)-0.5;zz=abs(z-0.5)-0.5;
   d1=max(xx,max(yy,zz));//distance to the box
   d=d1;//current computed distance
   p=1;
   for(m=1; m<MI ; m++) {

      xa = 3*x*p % 3;
      ya = 3*y*p % 3;
      za = 3*z*p % 3;
      p*=3;

      //we can also translate/rotate (xa,ya,za) without affecting the DE estimate

      xx=0.5-abs(xa-1.5);yy=0.5-abs(ya-1.5);zz=0.5-abs(za-1.5);
      d1=min(max(xx,zz),min(max(xx,yy),max(yy,zz)))/p;//distance inside the 3 axis aligned square tubes
      
      d=max(d,d1);//intersection
   }
   return d*2; //the distance estimate. The "*2" is because of the scaling we did at the begining of the function
}

//derived from Buddhi's algorithm
SphereSponge3(x, y, z) {//by recursively digging space
   //Same as for the Menger sponge but with spheres
   x+=1;y+=1;z+=1;
   intrad=param1;
   scl=3;mod=4;
   a=x;b=y;c=z;k=2;
   d=-100;
   for (L = 0; L < MI ; L++)
   {
     xx = a * k % mod - 0.5*mod;
     yy = b * k % mod - 0.5*mod;
     zz = c * k % mod - 0.5*mod;
     r2=xx*xx + yy*yy + zz*zz;
     d1=(intrad-sqrt(r2))/k;//distance to the edge of the sphere (positive inside)
     d=max(d,d1);//intersect
     
     k *= scl;
   }
   return d;// distance estimate
}

float DE(vec3 p)
{
	p=p*0.5+vec3(0.5);
	vec3 pp= abs(p-0.5)-0.5;
	float k=1.0;
	float d1 = max(pp.x,max(pp.y,pp.z));
	float d=d1;
	for (int i = 0; i < Iterations ; i++)
	{
		vec3 pa = mod(3.0*p*k, 3.0);
		k *= Scale;
		
		pp = 0.5-abs(pa-1.5)+Offset;
             pp*=rot;
		d1=min(max(pp.x,pp.z),min(max(pp.x,pp.y),max(pp.y,pp.z)))/k;//distance inside the 3 axis aligned square tubes
		d=max(d,d1);
		if (i<ColorIterations) orbitTrap = min(orbitTrap, abs(vec4(pp,dot(pp,pp))));
	
	}
		
	// Use this to crop to a sphere:
	//  float e = clamp(length(z)-2.0, 0.0,100.0);
	//  return max(d,e);// distance estimate
	return d;
}

float DE(vec3 p)
{
	p=p*0.5+vec3(0.5);
	vec3 pp= abs(p-0.5)-0.5;
	float k=1.0;
	float d1 = max(pp.x,max(pp.y,pp.z));
	float d=d1;
	for (int i = 0; i < Iterations ; i++)
	{
		vec3 pa = mod(3.0*p*k, 3.0);
		
		pp = 0.5-abs(pa-1.5)+Offset;
             pp*=rot;
		d1= (1/k) * min(max(pp.x,pp.z),min(max(pp.x,pp.y),max(pp.y,pp.z)))/k;//distance inside the 3 axis aligned square tubes
             
		d=max(d,d1); k *= Scale;
		if (i<ColorIterations) orbitTrap = min(orbitTrap, abs(vec4(pp,dot(pp,pp))));
	
	}
		
	// Use this to crop to a sphere:
	//  float e = clamp(length(z)-2.0, 0.0,100.0);
	//  return max(d,e);// distance estimate
	return d;
}