If you were to ask me to write some code to convert an int64 into ascii decimals, I'd start with a 20 character buffer (because int64 will never need more), loop to populate the buffer with ascii decimal digits from the lowest significant end, then once the loop has finished and we know how many digits, copy the buffer into its place.

I'd love to told that this method in the article is actually significantly more efficient than my possibly naïve approach.