1# fastrand
2
3[![Build](https://github.com/smol-rs/fastrand/workflows/CI/badge.svg)](
4https://github.com/smol-rs/fastrand/actions)
5[![License](https://img.shields.io/badge/license-Apache--2.0_OR_MIT-blue.svg)](
6https://github.com/smol-rs/fastrand)
7[![Cargo](https://img.shields.io/crates/v/fastrand.svg)](
8https://crates.io/crates/fastrand)
9[![Documentation](https://docs.rs/fastrand/badge.svg)](
10https://docs.rs/fastrand)
11
12A simple and fast random number generator.
13
14The implementation uses [Wyrand](https://github.com/wangyi-fudan/wyhash), a simple and fast
15generator but **not** cryptographically secure.
16
17## Examples
18
19Flip a coin:
20
21```rust
22if fastrand::bool() {
23    println!("heads");
24} else {
25    println!("tails");
26}
27```
28
29Generate a random `i32`:
30
31```rust
32let num = fastrand::i32(..);
33```
34
35Choose a random element in an array:
36
37```rust
38let v = vec![1, 2, 3, 4, 5];
39let i = fastrand::usize(..v.len());
40let elem = v[i];
41```
42
43Sample values from an array with `O(n)` complexity (`n` is the length of array):
44
45```rust
46fastrand::choose_multiple(vec![1, 4, 5].iter(), 2);
47fastrand::choose_multiple(0..20, 12);
48```
49
50Shuffle an array:
51
52```rust
53let mut v = vec![1, 2, 3, 4, 5];
54fastrand::shuffle(&mut v);
55```
56
57Generate a random `Vec` or `String`:
58
59```rust
60use std::iter::repeat_with;
61
62let v: Vec<i32> = repeat_with(|| fastrand::i32(..)).take(10).collect();
63let s: String = repeat_with(fastrand::alphanumeric).take(10).collect();
64```
65
66To get reproducible results on every run, initialize the generator with a seed:
67
68```rust
69// Pick an arbitrary number as seed.
70fastrand::seed(7);
71
72// Now this prints the same number on every run:
73println!("{}", fastrand::u32(..));
74```
75
76To be more efficient, create a new `Rng` instance instead of using the thread-local
77generator:
78
79```rust
80use std::iter::repeat_with;
81
82let rng = fastrand::Rng::new();
83let mut bytes: Vec<u8> = repeat_with(|| rng.u8(..)).take(10_000).collect();
84```
85
86This crate aims to expose a core set of useful randomness primitives. For more niche algorithms, consider using the [`fastrand-contrib`] crate alongside this one.
87
88# Features
89
90- `std` (enabled by default): Enables the `std` library. This is required for the global
91  generator and global entropy. Without this feature, [`Rng`] can only be instantiated using
92  the [`with_seed`](https://docs.rs/fastrand/latest/fastrand/struct.Rng.html#method.with_seed) method.
93- `js`: Assumes that WebAssembly targets are being run in a JavaScript environment.
94
95[`fastrand-contrib`]: https://crates.io/crates/fastrand-contrib
96
97## License
98
99Licensed under either of
100
101 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
102 * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
103
104at your option.
105
106#### Contribution
107
108Unless you explicitly state otherwise, any contribution intentionally submitted
109for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
110dual licensed as above, without any additional terms or conditions.
111