Any reasonable charting code is far more complex than FFTs, of which there are basically only two ways to straightforwardly implement. Of course there are lots

Any reasonable charting code is far more complex than FFTs, of which there are basically only two ways to straightforwardly implement. Of course there are lots of complications you can add such as cache-awareness which change that picture, but that's probably not 40 lines of C (though 40 lines is far more than necessary for a simple FFT)