y_abs = fabsf(y);
x_abs = fabsf(x);

if(!((y_abs > 0.0f) || (x_abs > 0.0f)))
  return 0.0;

if(y_abs < x_abs)
  z = y_abs / x_abs;
else
  z = x_abs / y_abs;

/* when ratio approaches the table resolution, the angle is */
/* best approximated with the argument itself... */
if(z < TAN_MAP_RES)
  base_angle = z;
else {
  /* find index and interpolation value */
  alpha = z * (float)TAN_MAP_SIZE;
  index = ((int)alpha) & 0xff;
  alpha -= (float)index;
  /* determine base angle based on quadrant and */
  /* add or subtract table value from base angle based on quadrant */
  base_angle  =  fast_atan_table[index];
  base_angle += (fast_atan_table[index + 1] - fast_atan_table[index]) * alpha;
}