Branch/performance

@BrettASwift @kadst43 would you mind reviewing?
I do actually do it for `y` below on line 10 (and for `z` on line 24).  Did you mean for me to do it for `maxWorldX`?  I hadn't stored that as a variable because it's not reused.  But if you think that makes the code look cleaner, I could add that since I doubt that the extra allocated memory would contribute significantly to our garbage collection issue.

Which would you prefer?