1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Interface to random number generators in Rust.
13 //! This is an experimental library which lives underneath the standard library
14 //! in its dependency chain. This library is intended to define the interface
15 //! for random number generation and also provide utilities around doing so. It
16 //! is not recommended to use this library directly, but rather the official
17 //! interface through `std::rand`.
19 // Do not remove on snapshot creation. Needed for bootstrap. (Issue #22364)
20 #![cfg_attr(stage0, feature(custom_attribute))]
21 #![crate_name = "rand"]
22 #![crate_type = "rlib"]
23 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
24 html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
25 html_root_url = "https://doc.rust-lang.org/nightly/",
26 html_playground_url = "https://play.rust-lang.org/")]
29 #![unstable(feature = "rand",
30 reason = "use `rand` from crates.io")]
31 #![feature(core_float)]
32 #![feature(core_slice_ext)]
34 #![feature(num_bits_bytes)]
35 #![feature(staged_api)]
38 #![cfg_attr(test, feature(test, rand, rustc_private, iter_order))]
42 #[cfg(test)] #[macro_use] extern crate std;
43 #[cfg(test)] #[macro_use] extern crate log;
45 use core::marker::PhantomData;
47 pub use isaac::{IsaacRng, Isaac64Rng};
48 pub use chacha::ChaChaRng;
50 use distributions::{Range, IndependentSample};
51 use distributions::range::SampleRange;
54 const RAND_BENCH_N: u64 = 100;
56 pub mod distributions;
62 /// A type that can be randomly generated using an `Rng`.
64 pub trait Rand : Sized {
65 /// Generates a random instance of this type using the specified source of
67 fn rand<R: Rng>(rng: &mut R) -> Self;
70 /// A random number generator.
71 pub trait Rng : Sized {
72 /// Return the next random u32.
74 /// This rarely needs to be called directly, prefer `r.gen()` to
76 // FIXME #7771: Should be implemented in terms of next_u64
77 fn next_u32(&mut self) -> u32;
79 /// Return the next random u64.
81 /// By default this is implemented in terms of `next_u32`. An
82 /// implementation of this trait must provide at least one of
83 /// these two methods. Similarly to `next_u32`, this rarely needs
84 /// to be called directly, prefer `r.gen()` to `r.next_u64()`.
85 fn next_u64(&mut self) -> u64 {
86 ((self.next_u32() as u64) << 32) | (self.next_u32() as u64)
89 /// Return the next random f32 selected from the half-open
90 /// interval `[0, 1)`.
92 /// By default this is implemented in terms of `next_u32`, but a
93 /// random number generator which can generate numbers satisfying
94 /// the requirements directly can overload this for performance.
95 /// It is required that the return value lies in `[0, 1)`.
97 /// See `Closed01` for the closed interval `[0,1]`, and
98 /// `Open01` for the open interval `(0,1)`.
99 fn next_f32(&mut self) -> f32 {
100 const MANTISSA_BITS: usize = 24;
101 const IGNORED_BITS: usize = 8;
102 const SCALE: f32 = (1u64 << MANTISSA_BITS) as f32;
104 // using any more than `MANTISSA_BITS` bits will
105 // cause (e.g.) 0xffff_ffff to correspond to 1
106 // exactly, so we need to drop some (8 for f32, 11
107 // for f64) to guarantee the open end.
108 (self.next_u32() >> IGNORED_BITS) as f32 / SCALE
111 /// Return the next random f64 selected from the half-open
112 /// interval `[0, 1)`.
114 /// By default this is implemented in terms of `next_u64`, but a
115 /// random number generator which can generate numbers satisfying
116 /// the requirements directly can overload this for performance.
117 /// It is required that the return value lies in `[0, 1)`.
119 /// See `Closed01` for the closed interval `[0,1]`, and
120 /// `Open01` for the open interval `(0,1)`.
121 fn next_f64(&mut self) -> f64 {
122 const MANTISSA_BITS: usize = 53;
123 const IGNORED_BITS: usize = 11;
124 const SCALE: f64 = (1u64 << MANTISSA_BITS) as f64;
126 (self.next_u64() >> IGNORED_BITS) as f64 / SCALE
129 /// Fill `dest` with random data.
131 /// This has a default implementation in terms of `next_u64` and
132 /// `next_u32`, but should be overridden by implementations that
133 /// offer a more efficient solution than just calling those
134 /// methods repeatedly.
136 /// This method does *not* have a requirement to bear any fixed
137 /// relationship to the other methods, for example, it does *not*
138 /// have to result in the same output as progressively filling
139 /// `dest` with `self.gen::<u8>()`, and any such behaviour should
140 /// not be relied upon.
142 /// This method should guarantee that `dest` is entirely filled
143 /// with new data, and may panic if this is impossible
144 /// (e.g. reading past the end of a file that is being used as the
145 /// source of randomness).
146 fn fill_bytes(&mut self, dest: &mut [u8]) {
147 // this could, in theory, be done by transmuting dest to a
148 // [u64], but this is (1) likely to be undefined behaviour for
149 // LLVM, (2) has to be very careful about alignment concerns,
150 // (3) adds more `unsafe` that needs to be checked, (4)
151 // probably doesn't give much performance gain if
152 // optimisations are on.
157 // we could micro-optimise here by generating a u32 if
158 // we only need a few more bytes to fill the vector
160 num = self.next_u64();
164 *byte = (num & 0xff) as u8;
170 /// Return a random value of a `Rand` type.
172 fn gen<T: Rand>(&mut self) -> T {
176 /// Return an iterator that will yield an infinite number of randomly
178 fn gen_iter<'a, T: Rand>(&'a mut self) -> Generator<'a, T, Self> {
179 Generator { rng: self, _marker: PhantomData }
182 /// Generate a random value in the range [`low`, `high`).
184 /// This is a convenience wrapper around
185 /// `distributions::Range`. If this function will be called
186 /// repeatedly with the same arguments, one should use `Range`, as
187 /// that will amortize the computations that allow for perfect
188 /// uniformity, as they only happen on initialization.
192 /// Panics if `low >= high`.
193 fn gen_range<T: PartialOrd + SampleRange>(&mut self, low: T, high: T) -> T {
194 assert!(low < high, "Rng.gen_range called with low >= high");
195 Range::new(low, high).ind_sample(self)
198 /// Return a bool with a 1 in n chance of true
199 fn gen_weighted_bool(&mut self, n: usize) -> bool {
200 n <= 1 || self.gen_range(0, n) == 0
203 /// Return an iterator of random characters from the set A-Z,a-z,0-9.
204 fn gen_ascii_chars<'a>(&'a mut self) -> AsciiGenerator<'a, Self> {
205 AsciiGenerator { rng: self }
208 /// Return a random element from `values`.
210 /// Return `None` if `values` is empty.
211 fn choose<'a, T>(&mut self, values: &'a [T]) -> Option<&'a T> {
212 if values.is_empty() {
215 Some(&values[self.gen_range(0, values.len())])
219 /// Shuffle a mutable slice in place.
220 fn shuffle<T>(&mut self, values: &mut [T]) {
221 let mut i = values.len();
223 // invariant: elements with index >= i have been locked in place.
225 // lock element i in place.
226 values.swap(i, self.gen_range(0, i + 1));
231 /// Iterator which will generate a stream of random items.
233 /// This iterator is created via the `gen_iter` method on `Rng`.
234 pub struct Generator<'a, T, R:'a> {
236 _marker: PhantomData<T>
239 impl<'a, T: Rand, R: Rng> Iterator for Generator<'a, T, R> {
242 fn next(&mut self) -> Option<T> {
247 /// Iterator which will continuously generate random ascii characters.
249 /// This iterator is created via the `gen_ascii_chars` method on `Rng`.
250 pub struct AsciiGenerator<'a, R:'a> {
254 impl<'a, R: Rng> Iterator for AsciiGenerator<'a, R> {
257 fn next(&mut self) -> Option<char> {
258 const GEN_ASCII_STR_CHARSET: &'static [u8] =
259 b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
260 abcdefghijklmnopqrstuvwxyz\
262 Some(*self.rng.choose(GEN_ASCII_STR_CHARSET).unwrap() as char)
266 /// A random number generator that can be explicitly seeded to produce
267 /// the same stream of randomness multiple times.
268 pub trait SeedableRng<Seed>: Rng {
269 /// Reseed an RNG with the given seed.
270 fn reseed(&mut self, Seed);
272 /// Create a new RNG with the given seed.
273 fn from_seed(seed: Seed) -> Self;
276 /// An Xorshift[1] random number
279 /// The Xorshift algorithm is not suitable for cryptographic purposes
280 /// but is very fast. If you do not know for sure that it fits your
281 /// requirements, use a more secure one such as `IsaacRng` or `OsRng`.
283 /// [1]: Marsaglia, George (July 2003). ["Xorshift
284 /// RNGs"](http://www.jstatsoft.org/v08/i14/paper). *Journal of
285 /// Statistical Software*. Vol. 8 (Issue 14).
287 pub struct XorShiftRng {
295 /// Creates a new XorShiftRng instance which is not seeded.
297 /// The initial values of this RNG are constants, so all generators created
298 /// by this function will yield the same stream of random numbers. It is
299 /// highly recommended that this is created through `SeedableRng` instead of
301 pub fn new_unseeded() -> XorShiftRng {
311 impl Rng for XorShiftRng {
313 fn next_u32(&mut self) -> u32 {
315 let t = x ^ (x << 11);
320 self.w = w ^ (w >> 19) ^ (t ^ (t >> 8));
325 impl SeedableRng<[u32; 4]> for XorShiftRng {
326 /// Reseed an XorShiftRng. This will panic if `seed` is entirely 0.
327 fn reseed(&mut self, seed: [u32; 4]) {
328 assert!(!seed.iter().all(|&x| x == 0),
329 "XorShiftRng.reseed called with an all zero seed.");
337 /// Create a new XorShiftRng. This will panic if `seed` is entirely 0.
338 fn from_seed(seed: [u32; 4]) -> XorShiftRng {
339 assert!(!seed.iter().all(|&x| x == 0),
340 "XorShiftRng::from_seed called with an all zero seed.");
351 impl Rand for XorShiftRng {
352 fn rand<R: Rng>(rng: &mut R) -> XorShiftRng {
353 let mut tuple: (u32, u32, u32, u32) = rng.gen();
354 while tuple == (0, 0, 0, 0) {
357 let (x, y, z, w) = tuple;
358 XorShiftRng { x: x, y: y, z: z, w: w }
362 /// A wrapper for generating floating point numbers uniformly in the
363 /// open interval `(0,1)` (not including either endpoint).
365 /// Use `Closed01` for the closed interval `[0,1]`, and the default
366 /// `Rand` implementation for `f32` and `f64` for the half-open
368 pub struct Open01<F>(pub F);
370 /// A wrapper for generating floating point numbers uniformly in the
371 /// closed interval `[0,1]` (including both endpoints).
373 /// Use `Open01` for the closed interval `(0,1)`, and the default
374 /// `Rand` implementation of `f32` and `f64` for the half-open
376 pub struct Closed01<F>(pub F);
380 use std::__rand as rand;
382 pub struct MyRng<R> { inner: R }
384 impl<R: rand::Rng> ::Rng for MyRng<R> {
385 fn next_u32(&mut self) -> u32 {
386 rand::Rng::next_u32(&mut self.inner)
390 pub fn rng() -> MyRng<rand::ThreadRng> {
391 MyRng { inner: rand::thread_rng() }
394 pub fn weak_rng() -> MyRng<rand::ThreadRng> {
395 MyRng { inner: rand::thread_rng() }