title: Negative numbers in fixed point format
body: <p>If I have a number <code>-1.101001_2 * 2^(-4)</code>, which is <code>-0.1025390625</code> in decimal, what is the correct fixed-point representation for this number?</p>
  <p>From what I have understood about fixed-point, this means it should be signed, so I thought that this would give a word length of 12 with a fraction length of 10, i.e.:</p>
  <pre><code>1   0    0001101001
  (s)        (frac)
  --- (word)-------
  </code></pre>
  <p>but this doesn't seem to be correct, as <code>100001101001</code> with word length of 12 and fraction length of 10 (1 signed bit) gives <code>-1.8975</code> instead.</p>
  <p>Did I make a mistake in the interpretation?</p>