BrowserUk,
I had originally always intended it to be an iterator but it would have made describing the algorithm more difficult. I made no effort at optimization so it can probably be improved greatly.

I have submitted a bug report on List::Util indicating that the documentation should be explicit about the single return value or the implementation should be changed. I suspect you are right and the fix is a doc update.

I have read through the perldeltas for 5.9.0 - 5.9.4 and did not see anything regarding sub call speedups.

I am interested in Benchmark results using real data. One optimization could be made by only handling 4 arrays and using a hardcode @cont of 4 instead of both being user defined.

You mentioned earlier not understanding tye's Algorithm::Loops. I won't pretend to understand his code either but I do understand the methodology. If you haven't seen Arbitrarily Nested Loops and NestedLoops and the Odometer Model, they may help explain it.