Comment by purplesyringa
2 days ago
The right-shift is the problem. You need to shift right by `j * 8`, which itself requires a shift to compute (`j << 3`), so you have two shifts on the critical path, resulting in a latency of 2 cycles. It's better than a load, but it's still noticeable.
2 cycles vs ~5 cycles is still nice improvement plus its more deterministic (but not that fast in optimistic case; better in pessimistic case) than `if` appraoch and probably easier to "invent" and reason about. Definitely not that cool as your `if` solution though :)