[uplifter]

You're absolutely right. The obvious solution would have been to create a boolean table containing all the pre-computed answers, and then simply use the integer you are testing as the index of the correct answer in memory. Now your isEven code is just a simple array lookup! Such an obvious improvement, I can't believe the OP didn't see it.

And with a little extra work you can shrink the whole table's size in memory by a factor of eight, but I'll leave that as an exercise for the interested reader.

[jiggawatts]

If the "exercise" is to strictly rely on if-else statements, then the obvious speedup is to perform a binary search instead of a linear one. The result would still be horrifically space inefficient, but the speed would be roughly the time it takes to load 32x 4KB pages randomly from disk (the article memory-mapped the file). On a modern SSD a random read is 20 microseconds, so that's less than a millisecond for an even/odd check!

"That's good enough, ship it to production. We'll optimise it later."

[mandarax8]

Maybe we can even find some correlation in the bit pattern of the input and the Boolean table!

[__david__]

Perhaps, but I fear you’re veering way too much into “clever” territory. Remember, this code has to be understandable to the junior members of the team! If you’re not careful you’ll end up with arcane operators, strange magic numbers, and a general unreadable mess.