I used a very simplified IK of this kind in my Spider Robot animation
in the IRTC.
You can look at the code to see how I did it.
I could also try to figure out some math for you if you really want
(but right now I have a terrible "brain laziness"...)
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
