Rand

A Rust library for random number generation.

Rand provides utilities to generate random numbers, to convert them to useful types and distributions, and some randomness-related algorithms.

The core random number generation traits of Rand live in the rand_core crate but are also exposed here; RNG implementations should prefer to use rand_core while most other users should depend on rand.

Documentation:

Usage

Add this to your Cargo.toml:

[dependencies]
rand = "0.6"

To get started using Rand, see The Book.

Versions

The Rand lib is not yet stable, however we are careful to limit breaking changes and warn via deprecation wherever possible. Patch versions never introduce breaking changes. The following minor versions are supported:

Version 0.6 was released in November 2018, redesigning the seq module, moving most PRNGs to external crates, and many small changes.
Version 0.5 was released in May 2018, as a major reorganisation (introducing RngCore and rand_core, and deprecating Rand and the previous distribution traits).
Version 0.4 was released in December 2017, but contained almost no breaking changes from the 0.3 series.

A detailed changelog is available.

When upgrading to the next minor series (especially 0.4 → 0.5), we recommend reading the Upgrade Guide.

Rust version requirements

Since version 0.5, Rand requires Rustc version 1.22 or greater. Rand 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.

Travis CI always has a build with a pinned version of Rustc matching the oldest supported Rust release. The current policy is that this can be updated in any Rand release if required, but the change must be noted in the changelog.

To avoid bumping the required version unnecessarily, we use a build.rs script to auto-detect the compiler version and enable certain features or change code paths automatically. Since this makes it easy to unintentionally make use of features requiring a more recent Rust version, we recommend testing with a pinned version of Rustc if you require compatibility with a specific version.

Crate Features

Rand is built with the std and rand_os features enabled by default:

std enables functionality dependent on the std lib and implies alloc and rand_os
rand_os enables the rand_os crate, rngs::OsRng and enables its usage; the continued existance of this feature is not guaranteed so users are encouraged to specify std instead

The following optional features are available:

alloc can be used instead of std to provide Vec and Box.
log enables some logging via the log crate.
nightly enables all unstable features (simd_support).
serde1 enables serialization for some types, via Serde version 1.
simd_support enables uniform sampling of SIMD types (integers and floats).
stdweb enables support for OsRng on wasm32-unknown-unknown via stdweb combined with cargo-web.
wasm-bindgen enables support for OsRng on wasm32-unknown-unknown via wasm-bindgen

no_std mode is activated by setting default-features = false; this removes functionality depending on std:

thread_rng(), and random() are not available, as they require thread-local storage and an entropy source.
OsRng and EntropyRng are unavailable.
JitterRng code is still present, but a nanosecond timer must be provided via JitterRng::new_with_timer
Since no external entropy is available, it is not possible to create generators with fresh seeds using the FromEntropy trait (user must provide a seed).
Several non-linear distributions distributions are unavailable since exp and log functions are not provided in core.
Large parts of the seq-uence module are unavailable, unless the alloc feature is used (several APIs and many implementations require Vec).

License

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