title: How is the gaussian filter algorithm work in OpenCV
body: <p>I write my own gaussian filter but it is really slow.</p>
  
  <p>OpenCV's Gaussian algorithm is much faster, 20 times than my gaussian filter. 
  I want to rewrite OpenCV's Gaussian algorithm in my project, and I don't want to include opencv in my project. </p>
  
  <p>However,</p>
  
  <blockquote>
    <p>Can anyone give me the algorithm description, opencv's source code
    seems too hard to understand?</p>
  </blockquote>