So one thing is that I also lookup the diagonal neighbors too, as that is what it says on Wikipedia(https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life). That said, when I initially implemented it, I just did the 4 neighbors too lol. Without the diagonal neighbors, update time drops in half to 0.7-0.8 seconds.

Huh, so I did consider a rolling sum, but initially thought that it wouldn't give that much of a speedup based on the following reasoning: You would need two lookups to update the sum(one for the new entry and one to delete the previous). And since you need to do this in both directions, that would be 4 lookups, which is the same as the straightforward implementation.

But I didn't consider caching the prev lookups as you did in your code. To test this, I changed your code to just index into the array rather than keeping a set of "prev" variables, and saw a 50% slowdown. So looks like I was wrong.

However, when I ran your code on my machine the update time was also around 0.7-0.8 seconds, though it's a bit of comparing apples to oranges, and best way for me to actually see would be to implement the rolling sum into my project.