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| </pre><pre class="rust"><code><span class="comment">// Copyright 2018 Developers of the Rand project. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| </span><span class="doccomment">//! A small fast RNG |
| |
| </span><span class="kw">use </span>rand_core::{Error, RngCore, SeedableRng}; |
| |
| <span class="attribute">#[cfg(target_pointer_width = <span class="string">"64"</span>)] |
| </span><span class="kw">type </span>Rng = <span class="kw">super</span>::xoshiro256plusplus::Xoshiro256PlusPlus; |
| <span class="attribute">#[cfg(not(target_pointer_width = <span class="string">"64"</span>))] |
| </span><span class="kw">type </span>Rng = <span class="kw">super</span>::xoshiro128plusplus::Xoshiro128PlusPlus; |
| |
| <span class="doccomment">/// A small-state, fast non-crypto PRNG |
| /// |
| /// `SmallRng` may be a good choice when a PRNG with small state, cheap |
| /// initialization, good statistical quality and good performance are required. |
| /// Note that depending on the application, [`StdRng`] may be faster on many |
| /// modern platforms while providing higher-quality randomness. Furthermore, |
| /// `SmallRng` is **not** a good choice when: |
| /// - Security against prediction is important. Use [`StdRng`] instead. |
| /// - Seeds with many zeros are provided. In such cases, it takes `SmallRng` |
| /// about 10 samples to produce 0 and 1 bits with equal probability. Either |
| /// provide seeds with an approximately equal number of 0 and 1 (for example |
| /// by using [`SeedableRng::from_entropy`] or [`SeedableRng::seed_from_u64`]), |
| /// or use [`StdRng`] instead. |
| /// |
| /// The algorithm is deterministic but should not be considered reproducible |
| /// due to dependence on platform and possible replacement in future |
| /// library versions. For a reproducible generator, use a named PRNG from an |
| /// external crate, e.g. [rand_xoshiro] or [rand_chacha]. |
| /// Refer also to [The Book](https://rust-random.github.io/book/guide-rngs.html). |
| /// |
| /// The PRNG algorithm in `SmallRng` is chosen to be efficient on the current |
| /// platform, without consideration for cryptography or security. The size of |
| /// its state is much smaller than [`StdRng`]. The current algorithm is |
| /// `Xoshiro256PlusPlus` on 64-bit platforms and `Xoshiro128PlusPlus` on 32-bit |
| /// platforms. Both are also implemented by the [rand_xoshiro] crate. |
| /// |
| /// # Examples |
| /// |
| /// Initializing `SmallRng` with a random seed can be done using [`SeedableRng::from_entropy`]: |
| /// |
| /// ``` |
| /// use rand::{Rng, SeedableRng}; |
| /// use rand::rngs::SmallRng; |
| /// |
| /// // Create small, cheap to initialize and fast RNG with a random seed. |
| /// // The randomness is supplied by the operating system. |
| /// let mut small_rng = SmallRng::from_entropy(); |
| /// # let v: u32 = small_rng.gen(); |
| /// ``` |
| /// |
| /// When initializing a lot of `SmallRng`'s, using [`thread_rng`] can be more |
| /// efficient: |
| /// |
| /// ``` |
| /// use rand::{SeedableRng, thread_rng}; |
| /// use rand::rngs::SmallRng; |
| /// |
| /// // Create a big, expensive to initialize and slower, but unpredictable RNG. |
| /// // This is cached and done only once per thread. |
| /// let mut thread_rng = thread_rng(); |
| /// // Create small, cheap to initialize and fast RNGs with random seeds. |
| /// // One can generally assume this won't fail. |
| /// let rngs: Vec<SmallRng> = (0..10) |
| /// .map(|_| SmallRng::from_rng(&mut thread_rng).unwrap()) |
| /// .collect(); |
| /// ``` |
| /// |
| /// [`StdRng`]: crate::rngs::StdRng |
| /// [`thread_rng`]: crate::thread_rng |
| /// [rand_chacha]: https://crates.io/crates/rand_chacha |
| /// [rand_xoshiro]: https://crates.io/crates/rand_xoshiro |
| </span><span class="attribute">#[cfg_attr(doc_cfg, doc(cfg(feature = <span class="string">"small_rng"</span>)))] |
| #[derive(Clone, Debug, PartialEq, Eq)] |
| </span><span class="kw">pub struct </span>SmallRng(Rng); |
| |
| <span class="kw">impl </span>RngCore <span class="kw">for </span>SmallRng { |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>next_u32(<span class="kw-2">&mut </span><span class="self">self</span>) -> u32 { |
| <span class="self">self</span>.<span class="number">0</span>.next_u32() |
| } |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>next_u64(<span class="kw-2">&mut </span><span class="self">self</span>) -> u64 { |
| <span class="self">self</span>.<span class="number">0</span>.next_u64() |
| } |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>fill_bytes(<span class="kw-2">&mut </span><span class="self">self</span>, dest: <span class="kw-2">&mut </span>[u8]) { |
| <span class="self">self</span>.<span class="number">0</span>.fill_bytes(dest); |
| } |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>try_fill_bytes(<span class="kw-2">&mut </span><span class="self">self</span>, dest: <span class="kw-2">&mut </span>[u8]) -> <span class="prelude-ty">Result</span><(), Error> { |
| <span class="self">self</span>.<span class="number">0</span>.try_fill_bytes(dest) |
| } |
| } |
| |
| <span class="kw">impl </span>SeedableRng <span class="kw">for </span>SmallRng { |
| <span class="kw">type </span>Seed = <Rng <span class="kw">as </span>SeedableRng>::Seed; |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>from_seed(seed: <span class="self">Self</span>::Seed) -> <span class="self">Self </span>{ |
| SmallRng(Rng::from_seed(seed)) |
| } |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>from_rng<R: RngCore>(rng: R) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>, Error> { |
| Rng::from_rng(rng).map(SmallRng) |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="rand" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
