121 lines
6.3 KiB
Markdown
121 lines
6.3 KiB
Markdown
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# Rand
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[](https://github.com/rust-random/rand/actions)
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[](https://crates.io/crates/rand)
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[](https://rust-random.github.io/book/)
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[](https://rust-random.github.io/rand/rand)
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[](https://docs.rs/rand)
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Rand is a set of crates supporting (pseudo-)random generators:
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- Built over a standard RNG trait: [`rand_core::RngCore`](https://docs.rs/rand_core/latest/rand_core/trait.RngCore.html)
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- With fast implementations of both [strong](https://rust-random.github.io/book/guide-rngs.html#cryptographically-secure-pseudo-random-number-generators-csprngs) and
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[small](https://rust-random.github.io/book/guide-rngs.html#basic-pseudo-random-number-generators-prngs) generators: [`rand::rngs`](https://docs.rs/rand/latest/rand/rngs/index.html), and more RNGs: [`rand_chacha`](https://docs.rs/rand_chacha), [`rand_xoshiro`](https://docs.rs/rand_xoshiro/), [`rand_pcg`](https://docs.rs/rand_pcg/), [rngs repo](https://github.com/rust-random/rngs/)
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- [`rand::rng`](https://docs.rs/rand/latest/rand/fn.rng.html) is an asymptotically-fast, automatically-seeded and reasonably strong generator available on all `std` targets
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- Direct support for seeding generators from the [getrandom] crate
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With broad support for random value generation and random processes:
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- [`StandardUniform`](https://docs.rs/rand/latest/rand/distr/struct.StandardUniform.html) random value sampling,
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[`Uniform`](https://docs.rs/rand/latest/rand/distr/struct.Uniform.html)-ranged value sampling
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and [more](https://docs.rs/rand/latest/rand/distr/index.html)
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- Samplers for a large number of non-uniform random number distributions via our own
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[`rand_distr`](https://docs.rs/rand_distr) and via
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the [`statrs`](https://docs.rs/statrs)
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- Random processes (mostly choose and shuffle) via [`rand::seq`](https://docs.rs/rand/latest/rand/seq/index.html) traits
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All with:
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- [Portably reproducible output](https://rust-random.github.io/book/portability.html)
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- `#[no_std]` compatibility (partial)
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- *Many* performance optimisations thanks to contributions from the wide
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user-base
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Rand **is not**:
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- Small (LoC). Most low-level crates are small, but the higher-level `rand`
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and `rand_distr` each contain a lot of functionality.
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- Simple (implementation). We have a strong focus on correctness, speed and flexibility, but
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not simplicity. If you prefer a small-and-simple library, there are
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alternatives including [fastrand](https://crates.io/crates/fastrand)
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and [oorandom](https://crates.io/crates/oorandom).
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- Primarily a cryptographic library. `rand` does provide some generators which
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aim to support unpredictable value generation under certain constraints;
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see [SECURITY.md](https://github.com/rust-random/rand/blob/master/SECURITY.md) for details.
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Users are expected to determine for themselves
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whether `rand`'s functionality meets their own security requirements.
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Documentation:
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- [The Rust Rand Book](https://rust-random.github.io/book)
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- [API reference (master branch)](https://rust-random.github.io/rand)
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- [API reference (docs.rs)](https://docs.rs/rand)
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## Versions
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Rand is *mature* (suitable for general usage, with infrequent breaking releases
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which minimise breakage) but not yet at 1.0. Current `MAJOR.MINOR` versions are:
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- Version 0.9 was released in January 2025.
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See the [CHANGELOG](https://github.com/rust-random/rand/blob/master/CHANGELOG.md) or [Upgrade Guide](https://rust-random.github.io/book/update.html) for more details.
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## Crate Features
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Rand is built with these features enabled by default:
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- `std` enables functionality dependent on the `std` lib
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- `alloc` (implied by `std`) enables functionality requiring an allocator
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- `os_rng` (implied by `std`) enables `rngs::OsRng`, using the [getrandom] crate
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- `std_rng` enables inclusion of `StdRng`, `ThreadRng`
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- `small_rng` enables inclusion of the `SmallRng` PRNG
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Optionally, the following dependencies can be enabled:
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- `log` enables logging via [log](https://crates.io/crates/log)
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Additionally, these features configure Rand:
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- `nightly` includes some additions requiring nightly Rust
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- `simd_support` (experimental) enables sampling of SIMD values
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(uniformly random SIMD integers and floats), requiring nightly Rust
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- `unbiased` use unbiased sampling for algorithms supporting this option: Uniform distribution.
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(By default, bias affecting no more than one in 2^48 samples is accepted.)
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Note: enabling this option is expected to affect reproducibility of results.
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Note that nightly features are not stable and therefore not all library and
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compiler versions will be compatible. This is especially true of Rand's
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experimental `simd_support` feature.
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Rand supports limited functionality in `no_std` mode (enabled via
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`default-features = false`). In this case, `OsRng` and `from_os_rng` are
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unavailable (unless `os_rng` is enabled), large parts of `seq` are
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unavailable (unless `alloc` is enabled), and `ThreadRng` is unavailable.
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## Portability and platform support
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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).
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The Rand library supports a variety of CPU architectures. Platform integration is outsourced to [getrandom].
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### WebAssembly support
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The [WASI](https://github.com/WebAssembly/WASI/tree/main) and Emscripten
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targets are directly supported. The `wasm32-unknown-unknown` target is not
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*automatically* supported. To enable support for this target, refer to the
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[`getrandom` documentation for WebAssembly](https://docs.rs/getrandom/latest/getrandom/#webassembly-support).
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Alternatively, the `os_rng` feature may be disabled.
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# License
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Rand is distributed under the terms of both the MIT license and the
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Apache License (Version 2.0).
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See [LICENSE-APACHE](https://github.com/rust-random/rand/blob/master/LICENSE-APACHE) and [LICENSE-MIT](https://github.com/rust-random/rand/blob/master/LICENSE-MIT), and
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[COPYRIGHT](https://github.com/rust-random/rand/blob/master/COPYRIGHT) for details.
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[getrandom]: https://crates.io/crates/getrandom
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