# Ryū

[<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)
[<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)
[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-ryu-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,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" height="20">](https://docs.rs/ryu)
[<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)

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 1.31; 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/1c413e127f8d02afd12eb6259bc80163722f1385

```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 Ryū 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>