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Dirty tricks 6502 programmers use (2019)
This post recaps some of the C64 coding tricks used in my little Commodore 64 coding competition. The competition rules were simple: make a C64 executable (PRG) that draws two lines to form the below image.
This CPU also doesn’t have a multiplier, so computing something like y*40+i usually involves either a bunch of logical shifts or a lookup table, again costing bytes. We keep adding the line slope to a fixed point counter yf and when the 8-bit addition sets the carry flag, add 40. Similarly, if you called any KERNAL ROM routines, you could totally take advantage of any side-effects they might have: returned CPU flags, temporary values set into zeropage, etc.
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