Do you think is ok to answer your own question with a "minor" optimization?
Note: this is a different case from that question because there is no previous answer and I am not aggregating suggestions.
I found in my own code space for optimization. Actually it could double the speed of the code for huge numbers but would not affect significantly small numbers. Until now, the question did not have any answer. Adding a comment would be very complex because the change was not marginal.
So, I posted my answer but I am still not sure if was a fair/good move.