[linux-audio-dev] Rectifier algorithm and Exponential FM question

Hi, Sorry if this is the wrong list. I have never found a list with people who can help me with these kind of questions. I am trying to figure out how a rectifier works in code. I have created something like it using tanh() distribution ( which will turn a sine wave into a sort-of-square wave). I can also achieve it with hard clipping/saturation. In the same sense I'd also like to know how a smooth operation works as well. I can not find any source code or explanations to help me figure out the algorithm yet. My other question is how are exponential signals generated? I want to experiment with exponential FM. My only understanding of Exp. Fm is that it sweeps half down and full up ( at 440hz, it would sweep 220hz down and 880 hz up). I haven't much of an idea how this is achieved. How do I convert a sine wave into an exponential signal for Exp FM?