title: Understanding two's complement
body: <p>I'm trying to understand two's complement:</p>
  
  <p>Does two's complement mean that this number is invalid:</p>
  
  <pre><code>1000
  </code></pre>
  
  <p>Does two's complement disallow the use of the most significant bit for positive numbers. Ie. Could</p>
  
  <pre><code>1000
  </code></pre>
  
  <p>Ever represent 2^3? Or would it represent -0?</p>
  
  <p>I'm also confused about why you need to add 1 to a one's complement.</p>