> I only have 64kB to play with, so it's important to be efficient.
If the author does not want to upgrade to the 1980s and the 65816 with its 16-bit accumulator, there is always the KimKlone for relieving the memory pressure somewhat.
* http://laughtonelectronics.com/Arcana/KimKlone/Kimklone_shor... (https://news.ycombinator.com/item?id=16564257)