111 lines
3.6 KiB
Markdown
111 lines
3.6 KiB
Markdown
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# Ryū
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[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/ryu-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/ryu)
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[<img alt="crates.io" src="https://img.shields.io/crates/v/ryu.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/ryu)
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[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-ryu-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/ryu)
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[<img alt="build status" src="https://img.shields.io/github/workflow/status/dtolnay/ryu/CI/master?style=for-the-badge" height="20">](https://github.com/dtolnay/ryu/actions?query=branch%3Amaster)
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Pure Rust implementation of Ryū, an algorithm to quickly convert floating point
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numbers to decimal strings.
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The PLDI'18 paper [*Ryū: fast float-to-string conversion*][paper] by Ulf Adams
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includes a complete correctness proof of the algorithm. The paper is available
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under the creative commons CC-BY-SA license.
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This Rust implementation is a line-by-line port of Ulf Adams' implementation in
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C, [https://github.com/ulfjack/ryu][upstream].
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*Requirements: this crate supports any compiler version back to rustc 1.36; it
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uses nothing from the Rust standard library so is usable from no_std crates.*
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[paper]: https://dl.acm.org/citation.cfm?id=3192369
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[upstream]: https://github.com/ulfjack/ryu/tree/abf76d252bc97300354857e64e80d4a2bf664291
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```toml
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[dependencies]
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ryu = "1.0"
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```
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<br>
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## Example
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```rust
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fn main() {
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let mut buffer = ryu::Buffer::new();
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let printed = buffer.format(1.234);
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assert_eq!(printed, "1.234");
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}
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```
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<br>
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## Performance (lower is better)
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You can run upstream's benchmarks with:
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```console
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$ git clone https://github.com/ulfjack/ryu c-ryu
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$ cd c-ryu
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$ bazel run -c opt //ryu/benchmark:ryu_benchmark
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```
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And the same benchmark against our implementation with:
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```console
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$ git clone https://github.com/dtolnay/ryu rust-ryu
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$ cd rust-ryu
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$ cargo run --example upstream_benchmark --release
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```
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These benchmarks measure the average time to print a 32-bit float and average
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time to print a 64-bit float, where the inputs are distributed as uniform random
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bit patterns 32 and 64 bits wide.
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The upstream C code, the unsafe direct Rust port, and the safe pretty Rust API
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all perform the same, taking around 21 nanoseconds to format a 32-bit float and
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31 nanoseconds to format a 64-bit float.
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There is also a Rust-specific benchmark comparing this implementation to the
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standard library which you can run with:
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```console
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$ cargo bench
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```
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The benchmark shows Ryū approximately 2-5x faster than the standard library
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across a range of f32 and f64 inputs. Measurements are in nanoseconds per
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iteration; smaller is better.
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## Formatting
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This library tends to produce more human-readable output than the standard
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library's to\_string, which never uses scientific notation. Here are two
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examples:
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- *ryu:* 1.23e40, *std:* 12300000000000000000000000000000000000000
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- *ryu:* 1.23e-40, *std:* 0.000000000000000000000000000000000000000123
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Both libraries print short decimals such as 0.0000123 without scientific
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notation.
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<br>
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#### License
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<sup>
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Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
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2.0</a> or <a href="LICENSE-BOOST">Boost Software License 1.0</a> at your
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option.
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</sup>
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<br>
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<sub>
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
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be dual licensed as above, without any additional terms or conditions.
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</sub>
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