Rand
A Rust library for random number generation, featuring:
- Easy random value generation and usage via the
Rng
,SliceRandom
andIteratorRandom
traits - Secure seeding via the
getrandom
crate and fast, convenient generation viathread_rng
- A modular design built over
rand_core
(see the book) - Fast implementations of the best-in-class cryptographic and non-cryptographic generators
- A flexible
distributions
module - Samplers for a large number of random number distributions via our own
rand_distr
and via thestatrs
- Portably reproducible output
#[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
andrand_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 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.
Documentation:
Usage
Add this to your Cargo.toml
:
[dependencies]
rand = "0.8.5"
To get started using Rand, see The Book.
Versions
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
from_entropy
toSeedableRng
, 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 RngCore
and SeedableRng
.) A few crate releases are thus compatibility shims,
depending on the next lib version (e.g. rand_core
versions 0.2.2
and
0.3.1
). This means, for example, that rand_core_0_4_0::SeedableRng
and
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.
Yanked versions
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.
Crate Features
Rand is built with these features enabled by default:
std
enables functionality dependent on thestd
liballoc
(implied bystd
) enables functionality requiring an allocatorgetrandom
(implied bystd
) is an optional dependency providing the code behindrngs::OsRng
std_rng
enables inclusion ofStdRng
,thread_rng
andrandom
(the latter two also require thatstd
be enabled)
Optionally, the following dependencies can be enabled:
log
enables logging via thelog
crate
Additionally, these features configure Rand:
small_rng
enables inclusion of theSmallRng
PRNGnightly
enables some optimizations requiring nightly Rustsimd_support
(experimental) enables sampling of SIMD values (uniformly random SIMD integers and floats), requiring nightly Rustmin_const_gen
enables 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
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.
WASM support
The WASM target wasm32-unknown-unknown
is not automatically supported by
rand
or getrandom
. To solve this, 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.
License
Rand is distributed under the terms of both the MIT license and the Apache License (Version 2.0).
See LICENSE-APACHE and LICENSE-MIT, and COPYRIGHT for details.