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https://github.com/rust-random/rand

A Rust library for random number generation.
https://github.com/rust-random/rand

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A Rust library for random number generation.

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# Rand



[![Test Status](https://github.com/rust-random/rand/workflows/Tests/badge.svg?event=push)](https://github.com/rust-random/rand/actions)

[![Crate](https://img.shields.io/crates/v/rand.svg)](https://crates.io/crates/rand)

[![Book](https://img.shields.io/badge/book-master-yellow.svg)](https://rust-random.github.io/book/)

[![API](https://img.shields.io/badge/api-master-yellow.svg)](https://rust-random.github.io/rand/rand)

[![API](https://docs.rs/rand/badge.svg)](https://docs.rs/rand)



A Rust library for random number generation, featuring:



-   Easy random value generation and usage via the [`Rng`](https://docs.rs/rand/*/rand/trait.Rng.html),

    [`SliceRandom`](https://docs.rs/rand/*/rand/seq/trait.SliceRandom.html) and

    [`IteratorRandom`](https://docs.rs/rand/*/rand/seq/trait.IteratorRandom.html) traits

-   Secure seeding via the [`getrandom` crate](https://crates.io/crates/getrandom)

    and fast, convenient generation via [`thread_rng`](https://docs.rs/rand/*/rand/fn.thread_rng.html)

-   A modular design built over [`rand_core`](https://crates.io/crates/rand_core)

    ([see the book](https://rust-random.github.io/book/crates.html))

-   Fast implementations of the best-in-class [cryptographic](https://rust-random.github.io/book/guide-rngs.html#cryptographically-secure-pseudo-random-number-generators-csprngs) and

    [non-cryptographic](https://rust-random.github.io/book/guide-rngs.html#basic-pseudo-random-number-generators-prngs) generators

-   A flexible [`distributions`](https://docs.rs/rand/*/rand/distributions/index.html) module

-   Samplers for a large number of random number distributions via our own

    [`rand_distr`](https://docs.rs/rand_distr) and via

    the [`statrs`](https://docs.rs/statrs/0.13.0/statrs/)

-   [Portably reproducible output](https://rust-random.github.io/book/portability.html)

-   `#[no_std]` compatibility (partial)

-   *Many* performance optimisations



It's also worth pointing out what `rand` *is not*:



-   Small. Most low-level crates are small, but the higher-level `rand` and

    `rand_distr` each contain a lot of functionality.

-   Simple (implementation). We have a strong focus on correctness, speed and flexibility, but

    not simplicity. If you prefer a small-and-simple library, there are

    alternatives including [fastrand](https://crates.io/crates/fastrand)

    and [oorandom](https://crates.io/crates/oorandom).

-   Slow. We take performance seriously, with considerations also for set-up

    time of new distributions, commonly-used parameters, and parameters of the

    current sampler.



Documentation:



-   [The Rust Rand Book](https://rust-random.github.io/book)

-   [API reference (master branch)](https://rust-random.github.io/rand)

-   [API reference (docs.rs)](https://docs.rs/rand)



## Usage



Add this to your `Cargo.toml`:



```toml

[dependencies]

rand = "0.8.5"

```



To get started using Rand, see [The Book](https://rust-random.github.io/book).



## Versions



Rand is *mature* (suitable for general usage, with infrequent breaking releases

which minimise breakage) but not yet at 1.0. Current versions are:



-   Version 0.8 was released in December 2020 with many small changes.

-   Version 0.9 is in development with many small changes.



See the [CHANGELOG](CHANGELOG.md) or [Upgrade Guide](https://rust-random.github.io/book/update.html) for more details.



## Crate Features



Rand is built with these features enabled by default:



-   `std` enables functionality dependent on the `std` lib

-   `alloc` (implied by `std`) enables functionality requiring an allocator

-   `getrandom` (implied by `std`) is an optional dependency providing the code

    behind `rngs::OsRng`

-   `std_rng` enables inclusion of `StdRng`, `thread_rng` and `random`

    (the latter two *also* require that `std` be enabled)



Optionally, the following dependencies can be enabled:



-   `log` enables logging via [log](https://crates.io/crates/log)



Additionally, these features configure Rand:



-   `small_rng` enables inclusion of the `SmallRng` PRNG

-   `nightly` includes some additions requiring nightly Rust

-   `simd_support` (experimental) enables sampling of SIMD values

    (uniformly random SIMD integers and floats), requiring nightly Rust



Note that nightly features are not stable and therefore not all library and

compiler versions will be compatible. This is especially true of Rand's

experimental `simd_support` feature.



Rand supports limited functionality in `no_std` mode (enabled via

`default-features = false`). In this case, `OsRng` and `from_entropy` are

unavailable (unless `getrandom` is enabled), large parts of `seq` are

unavailable (unless `alloc` is enabled), and `thread_rng` and `random` are

unavailable.



## Portability and platform support



Many (but not all) algorithms are intended to have reproducible output. Read more in the book: [Portability](https://rust-random.github.io/book/portability.html).



The Rand library supports a variety of CPU architectures. Platform integration is outsourced to [getrandom](https://docs.rs/getrandom/latest/getrandom/).



### WASM support



Seeding entropy from OS on WASM target `wasm32-unknown-unknown` is not

*automatically* supported by `rand` or `getrandom`. If you are fine with

seeding the generator manually, you can disable the `getrandom` feature

and use the methods on the `SeedableRng` trait. To enable seeding from OS,

either use a different target such as `wasm32-wasi` or add a direct

dependency on `getrandom` with the `js` feature (if the target supports

JavaScript). See

[getrandom#WebAssembly support](https://docs.rs/getrandom/latest/getrandom/#webassembly-support).



# License



Rand is distributed under the terms of both the MIT license and the

Apache License (Version 2.0).



See [LICENSE-APACHE](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT), and

[COPYRIGHT](COPYRIGHT) for details.