1# Ryū
2
3[<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)
4[<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)
5[<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)
6[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/ryu/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/ryu/actions?query=branch%3Amaster)
7
8Pure Rust implementation of Ryū, an algorithm to quickly convert floating point
9numbers to decimal strings.
10
11The PLDI'18 paper [*Ryū: fast float-to-string conversion*][paper] by Ulf Adams
12includes a complete correctness proof of the algorithm. The paper is available
13under the creative commons CC-BY-SA license.
14
15This Rust implementation is a line-by-line port of Ulf Adams' implementation in
16C, [https://github.com/ulfjack/ryu][upstream].
17
18*Requirements: this crate supports any compiler version back to rustc 1.36; it
19uses nothing from the Rust standard library so is usable from no_std crates.*
20
21[paper]: https://dl.acm.org/citation.cfm?id=3192369
22[upstream]: https://github.com/ulfjack/ryu/tree/77e767f5e056bab96e895072fc21618ecff2f44b
23
24```toml
25[dependencies]
26ryu = "1.0"
27```
28
29<br>
30
31## Example
32
33```rust
34fn main() {
35    let mut buffer = ryu::Buffer::new();
36    let printed = buffer.format(1.234);
37    assert_eq!(printed, "1.234");
38}
39```
40
41<br>
42
43## Performance (lower is better)
44
45![performance](https://raw.githubusercontent.com/dtolnay/ryu/master/performance.png)
46
47You can run upstream's benchmarks with:
48
49```console
50$ git clone https://github.com/ulfjack/ryu c-ryu
51$ cd c-ryu
52$ bazel run -c opt //ryu/benchmark:ryu_benchmark
53```
54
55And the same benchmark against our implementation with:
56
57```console
58$ git clone https://github.com/dtolnay/ryu rust-ryu
59$ cd rust-ryu
60$ cargo run --example upstream_benchmark --release
61```
62
63These benchmarks measure the average time to print a 32-bit float and average
64time to print a 64-bit float, where the inputs are distributed as uniform random
65bit patterns 32 and 64 bits wide.
66
67The upstream C code, the unsafe direct Rust port, and the safe pretty Rust API
68all perform the same, taking around 21 nanoseconds to format a 32-bit float and
6931 nanoseconds to format a 64-bit float.
70
71There is also a Rust-specific benchmark comparing this implementation to the
72standard library which you can run with:
73
74```console
75$ cargo bench
76```
77
78The benchmark shows Ryū approximately 2-5x faster than the standard library
79across a range of f32 and f64 inputs. Measurements are in nanoseconds per
80iteration; smaller is better.
81
82## Formatting
83
84This library tends to produce more human-readable output than the standard
85library's to\_string, which never uses scientific notation. Here are two
86examples:
87
88- *ryu:* 1.23e40, *std:* 12300000000000000000000000000000000000000
89- *ryu:* 1.23e-40, *std:* 0.000000000000000000000000000000000000000123
90
91Both libraries print short decimals such as 0.0000123 without scientific
92notation.
93
94<br>
95
96#### License
97
98<sup>
99Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
1002.0</a> or <a href="LICENSE-BOOST">Boost Software License 1.0</a> at your
101option.
102</sup>
103
104<br>
105
106<sub>
107Unless you explicitly state otherwise, any contribution intentionally submitted
108for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
109be dual licensed as above, without any additional terms or conditions.
110</sub>
111