cargo b --release
cargo r --release
target-cpu=native
gives around a 5% performance boost.
RUSTFLAGS="-C target-cpu=native" cargo bench
01 bytes time: [4.2423 us 4.2974 us 4.3527 us]
02 bytes time: [274.52 us 275.55 us 276.68 us]
03 bytes time: [20.334 ms 20.414 ms 20.500 ms]
04 bytes time: [1.6147 s 1.6206 s 1.6267 s]
05 bytes time: [127.16 s 131.32 s 135.23 s]