Repository files navigation

Rand is a set of crates supporting (pseudo-)random generators:

• Built over a standard RNG trait:rand_core::RngCore
• With fast implementations of bothstrong andsmall generators:rand::rngs, and more RNGs:rand_chacha,rand_xoshiro,rand_pcg,rngs repo
• rand::rng is an asymptotically-fast, automatically-seeded and reasonably strong generator available on allstd targets
• Direct support for seeding generators from thegetrandom crate

With broad support for random value generation and random processes:

• StandardUniform random value sampling,Uniform-ranged value samplingandmore
• Samplers for a large number of non-uniform random number distributions via our ownrand_distr and viathestatrs
• Random processes (mostly choose and shuffle) viarand::seq traits

All with:

• Portably reproducible output
• #[no_std] compatibility (partial)
• Many performance optimisations thanks to contributions from the wideuser-base

Randis not:

• Small (LoC). Most low-level crates are small, but the higher-levelrandandrand_distr each contain a lot of functionality.
• Simple (implementation). We have a strong focus on correctness, speed and flexibility, butnot simplicity. If you prefer a small-and-simple library, there arealternatives includingfastrandandoorandom.
• Primarily a cryptographic library.rand does provide some generators whichaim to support unpredictable value generation under certain constraints;seeSECURITY.md for details.Users are expected to determine for themselveswhetherrand's functionality meets their own security requirements.

Documentation:

• The Rust Rand Book
• API reference (master branch)
• API reference (docs.rs)

Rand ismature (suitable for general usage, with infrequent breaking releaseswhich minimise breakage) but not yet at 1.0. CurrentMAJOR.MINOR versions are:

• Version 0.9 was released in January 2025.

See theCHANGELOG orUpgrade Guide for more details.

Rand is built with these features enabled by default:

• std enables functionality dependent on thestd lib
• alloc (implied bystd) enables functionality requiring an allocator
• os_rng (implied bystd) enablesrngs::OsRng, using thegetrandom crate
• std_rng enables inclusion ofStdRng,ThreadRng
• small_rng enables inclusion of theSmallRng PRNG

Optionally, the following dependencies can be enabled:

• log enables logging vialog

Additionally, these features configure Rand:

• nightly includes some additions requiring nightly Rust

• simd_support (experimental) enables sampling of SIMD values(uniformly random SIMD integers and floats), requiring nightly Rust

• unbiased use unbiased sampling for algorithms supporting this option: Uniform distribution.

  (By default, bias affecting no more than one in 2^48 samples is accepted.)

  Note: enabling this option is expected to affect reproducibility of results.

Note that nightly features are not stable and therefore not all library andcompiler versions will be compatible. This is especially true of Rand'sexperimentalsimd_support feature.

Rand supports limited functionality inno_std mode (enabled viadefault-features = false). In this case,OsRng andfrom_os_rng areunavailable (unlessos_rng is enabled), large parts ofseq areunavailable (unlessalloc is enabled), andThreadRng is unavailable.

Many (but not all) algorithms are intended to have reproducible output. Read more in the book:Portability.

The Rand library supports a variety of CPU architectures. Platform integration is outsourced togetrandom.

TheWASI and Emscriptentargets are directly supported. Thewasm32-unknown-unknown target is notautomatically supported. To enable support for this target, refer to thegetrandom documentation for WebAssembly.Alternatively, theos_rng feature may be disabled.

Rand is distributed under the terms of both the MIT license and theApache License (Version 2.0).

SeeLICENSE-APACHE andLICENSE-MIT, andCOPYRIGHT for details.