# const-hex
[](https://github.com/danipopes/const-hex)
[](https://crates.io/crates/const-hex)
[](https://docs.rs/const-hex)
[](https://github.com/danipopes/const-hex/actions?query=branch%3Amaster)
This crate provides a fast conversion of byte arrays to hexadecimal strings,
both at compile time, and at run time.
It aims to be a drop-in replacement for the [`hex`] crate, as well as extending
the API with [const-eval], a [const-generics formatting buffer][buffer], similar
to [`itoa`]'s, and more.
_Version requirement: rustc 1.64+_
[const-eval]: https://docs.rs/const-hex/latest/const_hex/fn.const_encode.html
[buffer]: https://docs.rs/const-hex/latest/const_hex/struct.Buffer.html
[`itoa`]: https://docs.rs/itoa/latest/itoa/struct.Buffer.html
## Performance
This crate offers performance comparable to [`faster-hex`] on `x86`/`x86-64`
architectures but outperforms it on other platforms, as [`faster-hex`] is
only optimized for `x86`/`x86-64`.
This crate is 10 to 50 times faster than [`hex`] in encoding and decoding, and
100+ times faster than `libstd` in formatting.
The following benchmarks were ran on an AMD Ryzen 9 7950X, compiled with
`1.83.0-nightly (9e394f551 2024-09-25)` on `x86_64-unknown-linux-gnu`.
You can run these benchmarks with `cargo bench --features std` on a nightly
compiler.
```log
test check::const_hex::bench1_32b ... bench: 2.85 ns/iter (+/- 0.44)
test check::const_hex::bench2_256b ... bench: 15.36 ns/iter (+/- 0.44)
test check::const_hex::bench3_2k ... bench: 117.55 ns/iter (+/- 1.72)
test check::const_hex::bench4_16k ... bench: 915.78 ns/iter (+/- 56.34)
test check::const_hex::bench5_128k ... bench: 7,269.26 ns/iter (+/- 80.62)
test check::const_hex::bench6_1m ... bench: 58,975.63 ns/iter (+/- 707.02)
test check::faster_hex::bench1_32b ... bench: 2.70 ns/iter (+/- 0.01)
test check::faster_hex::bench2_256b ... bench: 14.45 ns/iter (+/- 1.44)
test check::faster_hex::bench3_2k ... bench: 123.58 ns/iter (+/- 1.09)
test check::faster_hex::bench4_16k ... bench: 960.32 ns/iter (+/- 6.34)
test check::faster_hex::bench5_128k ... bench: 7,709.14 ns/iter (+/- 77.69)
test check::faster_hex::bench6_1m ... bench: 62,165.54 ns/iter (+/- 1,167.78)
test check::naive::bench1_32b ... bench: 16.41 ns/iter (+/- 1.90)
test check::naive::bench2_256b ... bench: 221.25 ns/iter (+/- 3.47)
test check::naive::bench3_2k ... bench: 2,493.23 ns/iter (+/- 154.04)
test check::naive::bench4_16k ... bench: 16,221.81 ns/iter (+/- 384.98)
test check::naive::bench5_128k ... bench: 485,588.59 ns/iter (+/- 10,260.00)
test check::naive::bench6_1m ... bench: 3,895,089.20 ns/iter (+/- 45,589.05)
test decode::const_hex::bench1_32b ... bench: 17.33 ns/iter (+/- 0.38)
test decode::const_hex::bench2_256b ... bench: 38.17 ns/iter (+/- 1.07)
test decode::const_hex::bench3_2k ... bench: 235.07 ns/iter (+/- 3.27)
test decode::const_hex::bench4_16k ... bench: 1,681.14 ns/iter (+/- 17.25)
test decode::const_hex::bench5_128k ... bench: 13,097.65 ns/iter (+/- 101.14)
test decode::const_hex::bench6_1m ... bench: 105,945.60 ns/iter (+/- 2,703.49)
test decode::faster_hex::bench1_32b ... bench: 17.91 ns/iter (+/- 0.40)
test decode::faster_hex::bench2_256b ... bench: 54.53 ns/iter (+/- 1.41)
test decode::faster_hex::bench3_2k ... bench: 245.35 ns/iter (+/- 3.89)
test decode::faster_hex::bench4_16k ... bench: 1,836.62 ns/iter (+/- 25.01)
test decode::faster_hex::bench5_128k ... bench: 14,471.53 ns/iter (+/- 184.29)
test decode::faster_hex::bench6_1m ... bench: 116,688.27 ns/iter (+/- 1,539.72)
test decode::hex::bench1_32b ... bench: 109.14 ns/iter (+/- 1.88)
test decode::hex::bench2_256b ... bench: 712.92 ns/iter (+/- 14.25)
test decode::hex::bench3_2k ... bench: 5,196.66 ns/iter (+/- 102.67)
test decode::hex::bench4_16k ... bench: 41,308.30 ns/iter (+/- 917.60)
test decode::hex::bench5_128k ... bench: 786,648.00 ns/iter (+/- 6,589.60)
test decode::hex::bench6_1m ... bench: 6,316,271.50 ns/iter (+/- 22,712.18)
test decode_to_slice::const_hex::bench1_32b ... bench: 5.14 ns/iter (+/- 0.39)
test decode_to_slice::const_hex::bench2_256b ... bench: 26.18 ns/iter (+/- 0.26)
test decode_to_slice::const_hex::bench3_2k ... bench: 206.71 ns/iter (+/- 1.88)
test decode_to_slice::const_hex::bench4_16k ... bench: 1,666.49 ns/iter (+/- 15.67)
test decode_to_slice::const_hex::bench5_128k ... bench: 12,979.03 ns/iter (+/- 80.40)
test decode_to_slice::const_hex::bench6_1m ... bench: 107,213.20 ns/iter (+/- 4,024.91)
test decode_to_slice::faster_hex::bench1_32b ... bench: 6.51 ns/iter (+/- 0.04)
test decode_to_slice::faster_hex::bench2_256b ... bench: 28.66 ns/iter (+/- 0.29)
test decode_to_slice::faster_hex::bench3_2k ... bench: 217.84 ns/iter (+/- 1.03)
test decode_to_slice::faster_hex::bench4_16k ... bench: 1,730.89 ns/iter (+/- 19.36)
test decode_to_slice::faster_hex::bench5_128k ... bench: 13,439.63 ns/iter (+/- 92.19)
test decode_to_slice::faster_hex::bench6_1m ... bench: 109,432.90 ns/iter (+/- 1,526.01)
test decode_to_slice::hex::bench1_32b ... bench: 38.44 ns/iter (+/- 1.30)
test decode_to_slice::hex::bench2_256b ... bench: 290.78 ns/iter (+/- 16.09)
test decode_to_slice::hex::bench3_2k ... bench: 2,663.51 ns/iter (+/- 48.22)
test decode_to_slice::hex::bench4_16k ... bench: 19,016.95 ns/iter (+/- 514.35)
test decode_to_slice::hex::bench5_128k ... bench: 612,840.31 ns/iter (+/- 6,561.70)
test decode_to_slice::hex::bench6_1m ... bench: 5,098,572.75 ns/iter (+/- 120,113.94)
test encode::const_hex::bench1_32b ... bench: 6.94 ns/iter (+/- 0.06)
test encode::const_hex::bench2_256b ... bench: 11.84 ns/iter (+/- 0.07)
test encode::const_hex::bench3_2k ... bench: 78.36 ns/iter (+/- 0.89)
test encode::const_hex::bench4_16k ... bench: 475.29 ns/iter (+/- 11.56)
test encode::const_hex::bench5_128k ... bench: 3,577.27 ns/iter (+/- 70.48)
test encode::const_hex::bench6_1m ... bench: 29,996.00 ns/iter (+/- 668.44)
test encode::faster_hex::bench1_32b ... bench: 17.31 ns/iter (+/- 0.37)
test encode::faster_hex::bench2_256b ... bench: 39.39 ns/iter (+/- 0.76)
test encode::faster_hex::bench3_2k ... bench: 106.60 ns/iter (+/- 1.41)
test encode::faster_hex::bench4_16k ... bench: 653.21 ns/iter (+/- 5.40)
test encode::faster_hex::bench5_128k ... bench: 5,260.68 ns/iter (+/- 88.46)
test encode::faster_hex::bench6_1m ... bench: 44,520.36 ns/iter (+/- 1,200.74)
test encode::hex::bench1_32b ... bench: 102.77 ns/iter (+/- 0.82)
test encode::hex::bench2_256b ... bench: 720.90 ns/iter (+/- 22.52)
test encode::hex::bench3_2k ... bench: 5,672.44 ns/iter (+/- 287.53)
test encode::hex::bench4_16k ... bench: 38,988.71 ns/iter (+/- 6,457.99)
test encode::hex::bench5_128k ... bench: 364,376.25 ns/iter (+/- 51,416.85)
test encode::hex::bench6_1m ... bench: 2,959,499.88 ns/iter (+/- 410,006.38)
test encode_to_slice::const_hex::bench1_32b ... bench: 1.56 ns/iter (+/- 0.00)
test encode_to_slice::const_hex::bench2_256b ... bench: 6.75 ns/iter (+/- 0.03)
test encode_to_slice::const_hex::bench3_2k ... bench: 58.32 ns/iter (+/- 0.23)
test encode_to_slice::const_hex::bench4_16k ... bench: 518.24 ns/iter (+/- 4.91)
test encode_to_slice::const_hex::bench5_128k ... bench: 4,003.77 ns/iter (+/- 28.57)
test encode_to_slice::const_hex::bench6_1m ... bench: 34,519.64 ns/iter (+/- 656.35)
test encode_to_slice::faster_hex::bench1_32b ... bench: 4.54 ns/iter (+/- 0.01)
test encode_to_slice::faster_hex::bench2_256b ... bench: 8.11 ns/iter (+/- 0.05)
test encode_to_slice::faster_hex::bench3_2k ... bench: 52.10 ns/iter (+/- 0.64)
test encode_to_slice::faster_hex::bench4_16k ... bench: 475.81 ns/iter (+/- 6.50)
test encode_to_slice::faster_hex::bench5_128k ... bench: 3,425.49 ns/iter (+/- 15.01)
test encode_to_slice::faster_hex::bench6_1m ... bench: 28,725.82 ns/iter (+/- 839.95)
test encode_to_slice::hex::bench1_32b ... bench: 12.01 ns/iter (+/- 0.12)
test encode_to_slice::hex::bench2_256b ... bench: 121.68 ns/iter (+/- 1.98)
test encode_to_slice::hex::bench3_2k ... bench: 989.33 ns/iter (+/- 3.83)
test encode_to_slice::hex::bench4_16k ... bench: 8,087.93 ns/iter (+/- 25.25)
test encode_to_slice::hex::bench5_128k ... bench: 64,323.94 ns/iter (+/- 249.97)
test encode_to_slice::hex::bench6_1m ... bench: 515,710.80 ns/iter (+/- 2,232.59)
test format::const_hex::bench1_32b ... bench: 10.26 ns/iter (+/- 0.19)
test format::const_hex::bench2_256b ... bench: 18.28 ns/iter (+/- 0.86)
test format::const_hex::bench3_2k ... bench: 116.95 ns/iter (+/- 2.17)
test format::const_hex::bench4_16k ... bench: 1,122.29 ns/iter (+/- 6.25)
test format::const_hex::bench5_128k ... bench: 8,903.81 ns/iter (+/- 111.29)
test format::const_hex::bench6_1m ... bench: 77,476.15 ns/iter (+/- 1,498.93)
test format::std::bench1_32b ... bench: 370.27 ns/iter (+/- 2.52)
test format::std::bench2_256b ... bench: 2,910.66 ns/iter (+/- 40.35)
test format::std::bench3_2k ... bench: 22,554.52 ns/iter (+/- 263.93)
test format::std::bench4_16k ... bench: 182,692.06 ns/iter (+/- 3,494.64)
test format::std::bench5_128k ... bench: 1,475,988.90 ns/iter (+/- 21,895.90)
test format::std::bench6_1m ... bench: 11,834,234.60 ns/iter (+/- 139,230.20)
```
## Acknowledgements
- [`hex`] for the initial encoding/decoding implementations
- [`faster-hex`] for the `x86`/`x86-64` check and decode implementations
- [dtolnay]/[itoa] for the initial crate/library API layout
[`hex`]: https://crates.io/crates/hex
[`faster-hex`]: https://crates.io/crates/faster-hex
[dtolnay]: https://github.com/dtolnay
[itoa]: https://github.com/dtolnay/itoa
#### 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.