A Rust library for random number generation, featuring:
- Easy random value generation and usage via the
- Secure seeding via the
getrandomcrate and fast, convenient generation via
- A modular design built over
rand_core(see the book)
- Fast implementations of the best-in-class cryptographic and non-cryptographic generators
- A flexible
- Samplers for a large number of random number distributions via our own
rand_distrand via the
- Portably reproducible output
- 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_distreach 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 and 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.
Add this to your
 = "0.8.4"
To get started using Rand, see The Book.
Rand is mature (suitable for general usage, with infrequent breaking releases which minimise breakage) but not yet at 1.0. We maintain compatibility with pinned versions of the Rust compiler (see below).
Current Rand versions are:
- Version 0.7 was released in June 2019, moving most non-uniform distributions
to an external crate, moving
SeedableRng, and many small changes and fixes.
- Version 0.8 was released in December 2020 with many small changes.
A detailed changelog is available for releases.
When upgrading to the next minor series (especially 0.4 → 0.5), we recommend reading the Upgrade Guide.
Rand has not yet reached 1.0 implying some breaking changes may arrive in the future (SemVer allows each 0.x.0 release to include breaking changes), but is considered mature: breaking changes are minimised and breaking releases are infrequent.
Rand libs have inter-dependencies and make use of the
semver trick in order to make traits
compatible across crate versions. (This is especially important for
SeedableRng.) A few crate releases are thus compatibility shims,
depending on the next lib version (e.g.
0.3.1). This means, for example, that
rand_core_0_3_0::SeedableRng are distinct, incompatible traits, which can
cause build errors. Usually, running
cargo update is enough to fix any issues.
Some versions of Rand crates have been yanked ("unreleased"). Where this occurs,
the crate's CHANGELOG should be updated with a rationale, and a search on the
issue tracker with the keyword
yank should uncover the motivation.
Rust version requirements
Since version 0.8, Rand requires Rustc version 1.36 or greater. Rand 0.7 requires Rustc 1.32 or greater while versions 0.5 require Rustc 1.22 or greater, and 0.4 and 0.3 (since approx. June 2017) require Rustc version 1.15 or greater. Subsets of the Rand code may work with older Rust versions, but this is not supported.
Continuous Integration (CI) will always test the minimum supported Rustc version (the MSRV). The current policy is that this can be updated in any Rand release if required, but the change must be noted in the changelog.
Rand is built with these features enabled by default:
stdenables functionality dependent on the
std) enables functionality requiring an allocator
std) is an optional dependency providing the code behind
std_rngenables inclusion of
random(the latter two also require that
Optionally, the following dependencies can be enabled:
logenables logging via the
Additionally, these features configure Rand:
small_rngenables inclusion of the
nightlyenables some optimizations requiring nightly Rust
simd_support(experimental) enables sampling of SIMD values (uniformly random SIMD integers and floats), requiring nightly Rust
min_const_genenables generating random arrays of any size using min-const-generics, requiring Rust ≥ 1.51.
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
Rand supports limited functionality in
no_std mode (enabled via
default-features = false). In this case,
getrandom is enabled), large parts of
alloc is enabled), and
The WASM target
wasm32-unknown-unknown is not automatically supported by
getrandom. To solve this, either use a different target such as
wasm32-wasi or add a direct dependency on
getrandom with the
Rand is distributed under the terms of both the MIT license and the Apache License (Version 2.0).