title: Fast sigmoid algorithm
body: <p>The sigmoid function is defined as </p>
  
  <p><a href="https://i.stack.imgur.com/UxaaD.png" rel="noreferrer"><img src="https://i.stack.imgur.com/UxaaD.png" alt="enter image description here"></a></p>
  
  <p>I found that using the C built-in function <code>exp()</code> to calculate the value of <code>f(x)</code> is slow. Is there any faster algorithm to calculate the value of <code>f(x)</code>?</p>