http://benji3up2kxewkqfcq7buxk2xd6zwy3zggnurkrm3l4cvwy2iipvyyad.onion/mirrors/gmpdoc/Binary-to-Radix.html
Since the base case produces digits from least to most significant but they
want to be stored from most to least, it’s necessary to calculate in advance
how many digits there will be, or at least be sure not to underestimate that.