Crate ryu_js

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ECMAScript compliant 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.

§Example

let mut buffer = ryu_js::Buffer::new();
let printed = buffer.format(1.234);
assert_eq!(printed, "1.234");

§Performance (lower is better)

The 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:

$ cargo bench

The benchmark shows Ryū approximately 2-5x faster than the standard library across a range of f32 and f64 inputs. Measurements are in nanoseconds per iteration; smaller is better.

§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.

Modules§

  • raw
    Unsafe functions that mirror the API of the C implementation of Ryū.

Structs§

  • Buffer
    Safe API for formatting floating point numbers to text.

Traits§