title: Test if two floats are zero without multiple tests
body: <p>Is there a clever expression trick to test if a float vec3 is axial (i.e. two zero components) without using multiple equality tests?</p>
  
  <p>At first I thought of <code>if(abs(x)+abs(y)==0.0)</code> (pseudocode)... but of course each <code>abs</code> call probably does a branch/equality test.</p>
  
  <p>I thought of masking each float's bytes together and testing the result, but IEEE FP has both positive and negative 0.</p>