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diff --git a/third_party/rust/ryu/README.md b/third_party/rust/ryu/README.md new file mode 100644 index 0000000000..cc34dc2383 --- /dev/null +++ b/third_party/rust/ryu/README.md @@ -0,0 +1,114 @@ +# Ryū + +[](https://travis-ci.org/dtolnay/ryu) +[](https://crates.io/crates/ryu) +[](https://docs.rs/ryu) +[](https://blog.rust-lang.org/2017/02/02/Rust-1.15.html) + +Pure Rust implementation of Ryū, an algorithm to quickly convert floating point +numbers to decimal strings. + +The PLDI'18 paper [*Ryū: fast float-to-string conversion*][paper] by Ulf Adams +includes a complete correctness proof of the algorithm. The paper is available +under the creative commons CC-BY-SA license. + +This Rust implementation is a line-by-line port of Ulf Adams' implementation in +C, [https://github.com/ulfjack/ryu][upstream]. + +*Requirements: this crate supports any compiler version back to rustc 1.15; it +uses nothing from the Rust standard library so is usable from no_std crates.* + +[paper]: https://dl.acm.org/citation.cfm?id=3192369 +[upstream]: https://github.com/ulfjack/ryu/tree/688f43b62276b400728baad54afc32c3ab9c1a95 + +```toml +[dependencies] +ryu = "1.0" +``` + +## Example + +```rust +fn main() { + let mut buffer = ryu::Buffer::new(); + let printed = buffer.format(1.234); + assert_eq!(printed, "1.234"); +} +``` + +## Performance + +You can run upstream's benchmarks with: + +```console +$ git clone https://github.com/ulfjack/ryu c-ryu +$ cd c-ryu +$ bazel run -c opt //ryu/benchmark +``` + +And the same benchmark against our implementation with: + +```console +$ git clone https://github.com/dtolnay/ryu rust-ryu +$ cd rust-ryu +$ cargo run --example upstream_benchmark --release +``` + +These benchmarks measure the average time to print a 32-bit float and average +time to print a 64-bit float, where the inputs are distributed as uniform random +bit patterns 32 and 64 bits wide. + +The upstream C code, the unsafe direct Rust port, and the safe pretty Rust API +all perform the same, taking around 21 nanoseconds to format a 32-bit float and +31 nanoseconds to format a 64-bit float. + +There is also a Rust-specific benchmark comparing this implementation to the +standard library which you can run with: + +```console +$ cargo bench +``` + +The benchmark shows Ryu approximately 4-10x faster than the standard library +across a range of f32 and f64 inputs. Measurements are in nanoseconds per +iteration; smaller is better. + +| type=f32 | 0.0 | 0.1234 | 2.718281828459045 | f32::MAX | +|:--------:|:----:|:------:|:-----------------:|:--------:| +| RYU | 3ns | 28ns | 23ns | 22ns | +| STD | 40ns | 106ns | 128ns | 110ns | + +| type=f64 | 0.0 | 0.1234 | 2.718281828459045 | f64::MAX | +|:--------:|:----:|:------:|:-----------------:|:--------:| +| RYU | 3ns | 50ns | 35ns | 32ns | +| STD | 39ns | 105ns | 128ns | 202ns | + +## Formatting + +This library tends to produce more human-readable output than the standard +library's to\_string, which never uses scientific notation. Here are two +examples: + +- *ryu:* 1.23e40, *std:* 12300000000000000000000000000000000000000 +- *ryu:* 1.23e-40, *std:* 0.000000000000000000000000000000000000000123 + +Both libraries print short decimals such as 0.0000123 without scientific +notation. + +<br> + +#### License + +<sup> +Licensed under either of <a href="LICENSE-APACHE">Apache License, Version +2.0</a> or <a href="LICENSE-BOOST">Boost Software License 1.0</a> at your +option. +</sup> + +<br> + +<sub> +Unless you explicitly state otherwise, any contribution intentionally submitted +for inclusion in this crate by you, as defined in the Apache-2.0 license, shall +be dual licensed as above, without any additional terms or conditions. +</sub> |