It's good stuff - I would know, I found it in SCSP sources few months ago and it replaced my own floating-point based decoder smile
Truth be told all you need is quantization width data and the clipping values (127 & 24576) - it's all in docs. What isn't there is how this works on loops smile
As for those loops - I've just had a very nice idea, need to test it. Keep your fingers crossed, if this solves my little mystery it will also benefit your ADPCM code.