const-hex

This crate provides a fast conversion of byte arrays to hexadecimal strings, both at compile time, and at run time.

Extends the [hex] crate's implementation with [const-eval], a const-generics formatting buffer, similar to [itoa]'s, and more.

Version requirement: rustc 1.64+

Performance

This crate is 5 to 20 times faster than [hex] in encoding and decoding, and 30+ times faster than libstd in formatting.

The following benchmarks were ran on an AMD Ryzen 9 5900X, compiled with rustc 1.74.0-nightly (203c57dbe 2023-09-17) on x86_64-unknown-linux-gnu.

You can run these benchmarks with cargo bench --features std on a nightly compiler.

```log test decode::consthex::bench132 ... bench: 23 ns/iter (+/- 1) test decode::consthex::bench2256 ... bench: 98 ns/iter (+/- 4) test decode::consthex::bench32048 ... bench: 550 ns/iter (+/- 117) test decode::consthex::bench416384 ... bench: 4,104 ns/iter (+/- 35) test decode::hex::bench132 ... bench: 104 ns/iter (+/- 6) test decode::hex::bench2256 ... bench: 828 ns/iter (+/- 14) test decode::hex::bench32048 ... bench: 6,229 ns/iter (+/- 113) test decode::hex::bench416384 ... bench: 70,582 ns/iter (+/- 1,774)

test decodetoslice::consthex::bench132 ... bench: 12 ns/iter (+/- 1) test decodetoslice::consthex::bench2256 ... bench: 89 ns/iter (+/- 0) test decodetoslice::consthex::bench32048 ... bench: 678 ns/iter (+/- 15) test decodetoslice::consthex::bench416384 ... bench: 5,348 ns/iter (+/- 20) test decodetoslice::hex::bench132 ... bench: 57 ns/iter (+/- 0) test decodetoslice::hex::bench2256 ... bench: 515 ns/iter (+/- 43) test decodetoslice::hex::bench32048 ... bench: 4,021 ns/iter (+/- 173) test decodetoslice::hex::bench416384 ... bench: 54,224 ns/iter (+/- 2,023)

test encode::consthex::bench132 ... bench: 12 ns/iter (+/- 0) test encode::consthex::bench2256 ... bench: 25 ns/iter (+/- 1) test encode::consthex::bench32048 ... bench: 129 ns/iter (+/- 1) test encode::consthex::bench416384 ... bench: 854 ns/iter (+/- 8) test encode::hex::bench132 ... bench: 134 ns/iter (+/- 1) test encode::hex::bench2256 ... bench: 925 ns/iter (+/- 5) test encode::hex::bench32048 ... bench: 7,349 ns/iter (+/- 50) test encode::hex::bench416384 ... bench: 58,211 ns/iter (+/- 2,474)

test encodetoslice::consthex::bench132 ... bench: 1 ns/iter (+/- 0) test encodetoslice::consthex::bench2256 ... bench: 8 ns/iter (+/- 0) test encodetoslice::consthex::bench32048 ... bench: 70 ns/iter (+/- 0) test encodetoslice::consthex::bench416384 ... bench: 586 ns/iter (+/- 10) test encodetoslice::hex::bench132 ... bench: 14 ns/iter (+/- 0) test encodetoslice::hex::bench2256 ... bench: 130 ns/iter (+/- 3) test encodetoslice::hex::bench32048 ... bench: 794 ns/iter (+/- 1) test encodetoslice::hex::bench416384 ... bench: 6,401 ns/iter (+/- 9)

test format::consthex::bench132 ... bench: 11 ns/iter (+/- 0) test format::consthex::bench2256 ... bench: 27 ns/iter (+/- 0) test format::consthex::bench32048 ... bench: 173 ns/iter (+/- 0) test format::consthex::bench416384 ... bench: 1,409 ns/iter (+/- 7) test format::std::bench132 ... bench: 510 ns/iter (+/- 5) test format::std::bench2256 ... bench: 3,836 ns/iter (+/- 347) test format::std::bench32048 ... bench: 30,298 ns/iter (+/- 253) test format::std::bench416384 ... bench: 247,471 ns/iter (+/- 7,873) ```

Acknowledgements

[hex] for the initial encoding/decoding implementations
[dtolnay]/[itoa] for the initial crate/library API layout

License

^{Licensed under either of Apache License, Version
2.0 or MIT license at your option.}

_{Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in these crates by you, as defined in the Apache-2.0 license,
shall be dual licensed as above, without any additional terms or conditions.}