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