> Theoretically, if the code also for some reason needed to contain the original byte-value of the address at that offset The NES and Game Boy devices usually

> Theoretically, if the code also for some reason needed to contain the original byte-value of the address at that offset The NES and Game Boy devices usually needed this. Without it, bank-switching would result in one code changing several actual ROM bytes, when you only wanted to change one. The SNES almost never used bank switching so it wasn't necessary there. Still, it's not a one-way hash function here. If you were sufficiently bored, it would be very easy to deduce the encoding for at least the :value portion of the codes, just by comparing the codes in the book. I actually did something similar as a kid. If a phrase (as in a sentence of text) were illegal, using rot13 on it wouldn't make it legal. And Nintendo were chomping at the bit to ban/outlaw/block Game Genie devices (Nintendo has a sad history of being fiercely litigious against everyone), so I'm certain they would have gone for this had they thought they stood a chance at winning. That would be one hell of a jury trial, though. "They clearly reproduced the number 5, which was in our original game! It's obviously an illegal reproduction of our copyrighted game code!"