quaternion mean algorithm explained

hello! i'm a bit confused with reading this piece of code: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/doc/voicebox/rotqrmean.html i need to implement it in C++, can anyone help me with understanding arrays indexing etc. pseudo-code would be nice, i would convert it to C++ code myself, just need to clarify some things. not sure what i(r) and kx(ix) mean. these seem to be some kind of masks, but i'm not quite sure. thanks in advance!