# Crate ryu [−] [src]

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

    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 the same benchmark against our implementation with:

    $ 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:

    $ 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.

## 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

Float | A floating point number, f32 or f64, that can be written into a `ryu::Buffer`.