1# Rand 2 3[![Build Status](https://travis-ci.org/rust-lang-nursery/rand.svg?branch=master)](https://travis-ci.org/rust-lang-nursery/rand) 4[![Build Status](https://ci.appveyor.com/api/projects/status/github/rust-lang-nursery/rand?svg=true)](https://ci.appveyor.com/project/alexcrichton/rand) 5[![Latest version](https://img.shields.io/crates/v/rand.svg)](https://crates.io/crates/rand) 6[![Documentation](https://docs.rs/rand/badge.svg)](https://docs.rs/rand) 7[![Minimum rustc version](https://img.shields.io/badge/rustc-1.22+-yellow.svg)](https://github.com/rust-lang-nursery/rand#rust-version-requirements) 8 9A Rust library for random number generation. 10 11Rand provides utilities to generate random numbers, to convert them to useful 12types and distributions, and some randomness-related algorithms. 13 14The core random number generation traits of Rand live in the [rand_core]( 15https://crates.io/crates/rand_core) crate; this crate is most useful when 16implementing RNGs. 17 18API reference: 19[master branch](https://rust-lang-nursery.github.io/rand/rand/index.html), 20[by release](https://docs.rs/rand/0.5). 21 22## Usage 23 24Add this to your `Cargo.toml`: 25 26```toml 27[dependencies] 28rand = "0.5" 29``` 30 31and this to your crate root: 32 33```rust 34extern crate rand; 35 36use rand::prelude::*; 37 38fn main() { 39 // basic usage with random(): 40 let x: u8 = random(); 41 println!("{}", x); 42 43 let y = random::<f64>(); 44 println!("{}", y); 45 46 if random() { // generates a boolean 47 println!("Heads!"); 48 } 49 50 // normal usage needs both an RNG and a function to generate the appropriate 51 // type, range, distribution, etc. 52 let mut rng = thread_rng(); 53 if rng.gen() { // random bool 54 let x: f64 = rng.gen(); // random number in range [0, 1) 55 println!("x is: {}", x); 56 let ch = rng.gen::<char>(); // Sometimes you need type annotation 57 println!("char is: {}", ch); 58 println!("Number from 0 to 9: {}", rng.gen_range(0, 10)); 59 } 60} 61``` 62 63## Functionality 64 65The Rand crate provides: 66 67- A convenient to use default RNG, `thread_rng`: an automatically seeded, 68 crypto-grade generator stored in thread-local memory. 69- Pseudo-random number generators: `StdRng`, `SmallRng`, `prng` module. 70- Functionality for seeding PRNGs: the `FromEntropy` trait, and as sources of 71 external randomness `EntropyRng`, `OsRng` and `JitterRng`. 72- Most content from [`rand_core`](https://crates.io/crates/rand_core) 73 (re-exported): base random number generator traits and error-reporting types. 74- 'Distributions' producing many different types of random values: 75 - A `Standard` distribution for integers, floats, and derived types including 76 tuples, arrays and `Option` 77 - Unbiased sampling from specified `Uniform` ranges. 78 - Sampling from exponential/normal/gamma distributions. 79 - Sampling from binomial/poisson distributions. 80 - `gen_bool` aka Bernoulli distribution. 81- `seq`-uence related functionality: 82 - Sampling a subset of elements. 83 - Randomly shuffling a list. 84 85 86## Versions 87 88Version 0.5 is the latest version and contains many breaking changes. 89See [the Upgrade Guide](UPDATING.md) for guidance on updating from previous 90versions. 91 92Version 0.4 was released in December 2017. It contains almost no breaking 93changes since the 0.3 series. 94 95For more details, see the [changelog](CHANGELOG.md). 96 97### Rust version requirements 98 99The 0.5 release of Rand requires **Rustc version 1.22 or greater**. 100Rand 0.4 and 0.3 (since approx. June 2017) require Rustc version 1.15 or 101greater. Subsets of the Rand code may work with older Rust versions, but this 102is not supported. 103 104Travis CI always has a build with a pinned version of Rustc matching the oldest 105supported Rust release. The current policy is that this can be updated in any 106Rand release if required, but the change must be noted in the changelog. 107 108 109## Crate Features 110 111Rand is built with only the `std` feature enabled by default. The following 112optional features are available: 113 114- `alloc` can be used instead of `std` to provide `Vec` and `Box`. 115- `i128_support` enables support for generating `u128` and `i128` values. 116- `log` enables some logging via the `log` crate. 117- `nightly` enables all unstable features (`i128_support`). 118- `serde1` enables serialization for some types, via Serde version 1. 119- `stdweb` enables support for `OsRng` on `wasm-unknown-unknown` via `stdweb` 120 combined with `cargo-web`. 121 122`no_std` mode is activated by setting `default-features = false`; this removes 123functionality depending on `std`: 124 125- `thread_rng()`, and `random()` are not available, as they require thread-local 126 storage and an entropy source. 127- `OsRng` and `EntropyRng` are unavailable. 128- `JitterRng` code is still present, but a nanosecond timer must be provided via 129 `JitterRng::new_with_timer` 130- Since no external entropy is available, it is not possible to create 131 generators with fresh seeds using the `FromEntropy` trait (user must provide 132 a seed). 133- Exponential, normal and gamma type distributions are unavailable since `exp` 134 and `log` functions are not provided in `core`. 135- The `seq`-uence module is unavailable, as it requires `Vec`. 136 137 138# License 139 140Rand is distributed under the terms of both the MIT license and the 141Apache License (Version 2.0). 142 143See [LICENSE-APACHE](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT) for details. 144