commit | 65b99bbcb87b80f50a1f4b798cc1c6f7ab260de7 | [log] [tgz] |
---|---|---|
author | Xin Li <delphij@google.com> | Sat Feb 20 11:41:40 2021 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Sat Feb 20 11:41:40 2021 +0000 |
tree | 20577b756f45c418a4746c9051bd5418266d8b69 | |
parent | f1de93b9059679c543fe192c643e32d817e4092a [diff] | |
parent | 61371b04cf677d93f4d3ce456a5ce0ba348a901e [diff] |
[automerger skipped] Mark ab/7061308 as merged in stage. am: 61371b04cf -s ours am skip reason: Change-Id I1fddd0c8d8bd81cd9aabfd7fc3490594caf083d6 with SHA-1 e73de2d128 is in history Original change: undetermined MUST ONLY BE SUBMITTED BY AUTOMERGER Change-Id: Ic0f445c77ad524875c4085c32242ad642c2db676
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.
Requirements: this crate supports any compiler version back to rustc 1.31; it uses nothing from the Rust standard library so is usable from no_std crates.
[dependencies] ryu = "1.0"
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:
$ 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 |
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.