# 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.
| RYU | 3ns | 28ns | 23ns | 22ns |
| STD | 40ns | 106ns | 128ns | 110ns |
| 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>