title: How to implement borrow flag in C
body: <p>How to calculate borrow flag by subtracting two 8 bit numbers ?</p>
  
  <p>I found this borrow flag description but I still can't understand how to do it?</p>
  
  <blockquote>
    <p>The carry (borrow) flag is also set if the subtraction of two numbers 
    equires a borrow into the most significant (leftmost) bits subtracted.</p>
  </blockquote>
  
  <p>I think I need one-liner. Because calculating using loop is big bottleneck. Would be nice to see explanation how borrow flag works.</p>
  
  <p>Thanks.</p>