performance improvement

[LuoZijun]

Hi, i just tried to write a base64 codec and the performance has improved compared to your project.

feel free review code or copy code to this project :)

Code: https://github.com/shadowsocks/crypto2/blob/dev/src/base64.rs

Result:

// Your Project
test base64::bench_crate_decode     ... bench:          31 ns/iter (+/- 5)
test base64::bench_crate_encode     ... bench:          14 ns/iter (+/- 1)
// Me
test base64::bench_decode           ... bench:           7 ns/iter (+/- 2)
test base64::bench_encode           ... bench:           4 ns/iter (+/- 0)

[marshallpierce]

That's great! I'm squeezed for time right now so it'll be a while until I get to it, but thanks for the contribution!

[dkomanov]

I don't know if you did any performance improvements since, but I did a benchmarks and base64 clearly faster than crypto2's implementation: https://dkomanov.medium.com/base64-encoding-performance-java-vs-rust-c59f438411f0.