Math Behind Photoshop Blending

If you are a graphics programmer in the game industry, you will always have your beloved artists say something like this: "Hey, I want this Photoshop blaa-blaa-blending in our game!"

Then you will go to this link as I did for the overlay blend mode: http://www.nathanm.com/photoshop-blending-math/

Update: Found another article on ziggyware here: http://www.ziggyware.com/readarticle.php?article_id=228

Update:

the only link that's still alive: http://mouaif.wordpress.com/2009/01/05/photoshop-math-with-glsl-shaders