gecko-dev/third_party/rust/ryu

Ryū

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.

[dependencies]
ryu = "0.2"

Examples

extern crate ryu;

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:

$ git clone https://github.com/ulfjack/ryu c-ryu
$ cd c-ryu
$ bazel run -c opt //ryu/benchmark

And our benchmarks with:

$ git clone https://github.com/ulfjack/ryu rust-ryu
$ cd rust-ryu
$ cargo run --example 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.

License

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)