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 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. The ryu::raw module exposes
exactly the API and formatting of the C implementation as unsafe pure Rust
functions. There is additionally a safe API as demonstrated in the example code
below. The safe API uses the same underlying Ryū algorithm but diverges from the
formatting of the C implementation to produce more human-readable output, for
example 0.3 rather than 3E-1.
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.
toml
[dependencies]
ryu = "0.2"
rust
fn main() {
let mut buffer = ryu::Buffer::new();
let printed = buffer.format(1.234);
assert_eq!(printed, "1.234");
}
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 |
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:
Both libraries print short decimals such as 0.0000123 without scientific notation.
Licensed under either of the following at your option.