#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <math.h>
#include "output.h"


void circle2(int r) 
{
  int x = 0;
  int y = r;
  int d = -r;			/* d = x^2 + y^2 - r^2 - y */
  /* Precondition */
  assert(r >= 0);
  output8(x, y);
  while(x < y) {
    d += 2 * x + 1;		/* d' = d + 2 * x + 1 */
    x += 1;
    if(d > 0) {			/* d'-d'' = 2 * y */
      y -= 1;
      d += -2 * y;  /* d'' = d' - 2 * y + 1 = d + 2 * x - 2 * y + 1 */
    }
#if DEBUG
    { 
      int d0 = x*x + y*y-r*r -y;
      if(d != d0) {
	fprintf(stderr, "x=%d, y=%d, d=%d, should be d=%d\n", x, y, d, d0);
      }
    }
#endif
    output8(x, y);
  }
}