| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="A random number generator that can be explicitly seeded."><meta name="keywords" content="rust, rustlang, rust-lang, SeedableRng"><title>SeedableRng in rand_core - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" href="https://www.rust-lang.org/favicon.ico"></head><body class="rustdoc trait"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../rand_core/index.html"><div class="logo-container"><img src="https://www.rust-lang.org/logos/rust-logo-128x128-blk.png" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../rand_core/index.html"><div class="logo-container"> |
| <img src="https://www.rust-lang.org/logos/rust-logo-128x128-blk.png" alt="logo"></div></a><h2 class="location"><a href="#">SeedableRng</a></h2><div class="sidebar-elems"><section><h3><a href="#required-associated-types">Required Associated Types</a></h3><ul class="block"><li><a href="#associatedtype.Seed">Seed</a></li></ul><h3><a href="#required-methods">Required Methods</a></h3><ul class="block"><li><a href="#tymethod.from_seed">from_seed</a></li></ul><h3><a href="#provided-methods">Provided Methods</a></h3><ul class="block"><li><a href="#method.from_entropy">from_entropy</a></li><li><a href="#method.from_rng">from_rng</a></li><li><a href="#method.seed_from_u64">seed_from_u64</a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><h2><a href="index.html">In rand_core</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Trait <a href="index.html">rand_core</a>::<wbr><a class="trait" href="#">SeedableRng</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/rand_core/lib.rs.html#246-419">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust trait"><code>pub trait SeedableRng: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a> { |
| type <a href="#associatedtype.Seed" class="associatedtype">Seed</a>: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/default/trait.Default.html" title="trait core::default::Default">Default</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/convert/trait.AsMut.html" title="trait core::convert::AsMut">AsMut</a><[<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u8.html">u8</a>]>; |
| |
| fn <a href="#tymethod.from_seed" class="fnname">from_seed</a>(seed: Self::<a class="associatedtype" href="trait.SeedableRng.html#associatedtype.Seed" title="type rand_core::SeedableRng::Seed">Seed</a>) -> Self; |
| |
| fn <a href="#method.seed_from_u64" class="fnname">seed_from_u64</a>(state: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u64.html">u64</a>) -> Self { ... } |
| <span class="item-spacer"></span> fn <a href="#method.from_rng" class="fnname">from_rng</a><R: <a class="trait" href="trait.RngCore.html" title="trait rand_core::RngCore">RngCore</a>>(rng: R) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><Self, <a class="struct" href="struct.Error.html" title="struct rand_core::Error">Error</a>> { ... } |
| <span class="item-spacer"></span> fn <a href="#method.from_entropy" class="fnname">from_entropy</a>() -> Self { ... } |
| }</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A random number generator that can be explicitly seeded.</p> |
| <p>This trait encapsulates the low-level functionality common to all |
| pseudo-random number generators (PRNGs, or algorithmic generators).</p> |
| </div></details><h2 id="required-associated-types" class="small-section-header">Required Associated Types<a href="#required-associated-types" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle method-toggle" open><summary><section id="associatedtype.Seed" class="method has-srclink"><a class="srclink rightside" href="../src/rand_core/lib.rs.html#292">source</a><h4 class="code-header">type <a href="#associatedtype.Seed" class="associatedtype">Seed</a>: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/default/trait.Default.html" title="trait core::default::Default">Default</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/convert/trait.AsMut.html" title="trait core::convert::AsMut">AsMut</a><[<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u8.html">u8</a>]></h4></section></summary><div class="docblock"><p>Seed type, which is restricted to types mutably-dereferenceable as <code>u8</code> |
| arrays (we recommend <code>[u8; N]</code> for some <code>N</code>).</p> |
| <p>It is recommended to seed PRNGs with a seed of at least circa 100 bits, |
| which means an array of <code>[u8; 12]</code> or greater to avoid picking RNGs with |
| partially overlapping periods.</p> |
| <p>For cryptographic RNG’s a seed of 256 bits is recommended, <code>[u8; 32]</code>.</p> |
| <h5 id="implementing-seedablerng-for-rngs-with-large-seeds"><a href="#implementing-seedablerng-for-rngs-with-large-seeds">Implementing <code>SeedableRng</code> for RNGs with large seeds</a></h5> |
| <p>Note that the required traits <code>core::default::Default</code> and |
| <code>core::convert::AsMut<u8></code> are not implemented for large arrays |
| <code>[u8; N]</code> with <code>N</code> > 32. To be able to implement the traits required by |
| <code>SeedableRng</code> for RNGs with such large seeds, the newtype pattern can be |
| used:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand_core::SeedableRng; |
| |
| <span class="kw">const </span>N: usize = <span class="number">64</span>; |
| <span class="kw">pub struct </span>MyRngSeed(<span class="kw">pub </span>[u8; N]); |
| <span class="kw">pub struct </span>MyRng(MyRngSeed); |
| |
| <span class="kw">impl </span>Default <span class="kw">for </span>MyRngSeed { |
| <span class="kw">fn </span>default() -> MyRngSeed { |
| MyRngSeed([<span class="number">0</span>; N]) |
| } |
| } |
| |
| <span class="kw">impl </span>AsMut<[u8]> <span class="kw">for </span>MyRngSeed { |
| <span class="kw">fn </span>as_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>[u8] { |
| <span class="kw-2">&mut </span><span class="self">self</span>.<span class="number">0 |
| </span>} |
| } |
| |
| <span class="kw">impl </span>SeedableRng <span class="kw">for </span>MyRng { |
| <span class="kw">type </span>Seed = MyRngSeed; |
| |
| <span class="kw">fn </span>from_seed(seed: MyRngSeed) -> MyRng { |
| MyRng(seed) |
| } |
| }</code></pre></div> |
| </div></details></div><h2 id="required-methods" class="small-section-header">Required Methods<a href="#required-methods" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle method-toggle" open><summary><section id="tymethod.from_seed" class="method has-srclink"><a class="srclink rightside" href="../src/rand_core/lib.rs.html#319">source</a><h4 class="code-header">fn <a href="#tymethod.from_seed" class="fnname">from_seed</a>(seed: Self::<a class="associatedtype" href="trait.SeedableRng.html#associatedtype.Seed" title="type rand_core::SeedableRng::Seed">Seed</a>) -> Self</h4></section></summary><div class="docblock"><p>Create a new PRNG using the given seed.</p> |
| <p>PRNG implementations are allowed to assume that bits in the seed are |
| well distributed. That means usually that the number of one and zero |
| bits are roughly equal, and values like 0, 1 and (size - 1) are unlikely. |
| Note that many non-cryptographic PRNGs will show poor quality output |
| if this is not adhered to. If you wish to seed from simple numbers, use |
| <code>seed_from_u64</code> instead.</p> |
| <p>All PRNG implementations should be reproducible unless otherwise noted: |
| given a fixed <code>seed</code>, the same sequence of output should be produced |
| on all runs, library versions and architectures (e.g. check endianness). |
| Any “value-breaking” changes to the generator should require bumping at |
| least the minor version and documentation of the change.</p> |
| <p>It is not required that this function yield the same state as a |
| reference implementation of the PRNG given equivalent seed; if necessary |
| another constructor replicating behaviour from a reference |
| implementation can be added.</p> |
| <p>PRNG implementations should make sure <code>from_seed</code> never panics. In the |
| case that some special values (like an all zero seed) are not viable |
| seeds it is preferable to map these to alternative constant value(s), |
| for example <code>0xBAD5EEDu32</code> or <code>0x0DDB1A5E5BAD5EEDu64</code> (“odd biases? bad |
| seed”). This is assuming only a small number of values must be rejected.</p> |
| </div></details></div><h2 id="provided-methods" class="small-section-header">Provided Methods<a href="#provided-methods" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.seed_from_u64" class="method has-srclink"><a class="srclink rightside" href="../src/rand_core/lib.rs.html#335-364">source</a><h4 class="code-header">fn <a href="#method.seed_from_u64" class="fnname">seed_from_u64</a>(state: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u64.html">u64</a>) -> Self</h4></section></summary><div class="docblock"><p>Create a new PRNG using a <code>u64</code> seed.</p> |
| <p>This is a convenience-wrapper around <code>from_seed</code> to allow construction |
| of any <code>SeedableRng</code> from a simple <code>u64</code> value. It is designed such that |
| low Hamming Weight numbers like 0 and 1 can be used and should still |
| result in good, independent seeds to the PRNG which is returned.</p> |
| <p>This <strong>is not suitable for cryptography</strong>, as should be clear given that |
| the input size is only 64 bits.</p> |
| <p>Implementations for PRNGs <em>may</em> provide their own implementations of |
| this function, but the default implementation should be good enough for |
| all purposes. <em>Changing</em> the implementation of this function should be |
| considered a value-breaking change.</p> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.from_rng" class="method has-srclink"><a class="srclink rightside" href="../src/rand_core/lib.rs.html#390-394">source</a><h4 class="code-header">fn <a href="#method.from_rng" class="fnname">from_rng</a><R: <a class="trait" href="trait.RngCore.html" title="trait rand_core::RngCore">RngCore</a>>(rng: R) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><Self, <a class="struct" href="struct.Error.html" title="struct rand_core::Error">Error</a>></h4></section></summary><div class="docblock"><p>Create a new PRNG seeded from another <code>Rng</code>.</p> |
| <p>This may be useful when needing to rapidly seed many PRNGs from a master |
| PRNG, and to allow forking of PRNGs. It may be considered deterministic.</p> |
| <p>The master PRNG should be at least as high quality as the child PRNGs. |
| When seeding non-cryptographic child PRNGs, we recommend using a |
| different algorithm for the master PRNG (ideally a CSPRNG) to avoid |
| correlations between the child PRNGs. If this is not possible (e.g. |
| forking using small non-crypto PRNGs) ensure that your PRNG has a good |
| mixing function on the output or consider use of a hash function with |
| <code>from_seed</code>.</p> |
| <p>Note that seeding <code>XorShiftRng</code> from another <code>XorShiftRng</code> provides an |
| extreme example of what can go wrong: the new PRNG will be a clone |
| of the parent.</p> |
| <p>PRNG implementations are allowed to assume that a good RNG is provided |
| for seeding, and that it is cryptographically secure when appropriate. |
| As of <code>rand</code> 0.7 / <code>rand_core</code> 0.5, implementations overriding this |
| method should ensure the implementation satisfies reproducibility |
| (in prior versions this was not required).</p> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.from_entropy" class="method has-srclink"><a class="srclink rightside" href="../src/rand_core/lib.rs.html#412-418">source</a><h4 class="code-header">fn <a href="#method.from_entropy" class="fnname">from_entropy</a>() -> Self</h4></section></summary><div class="docblock"><p>Creates a new instance of the RNG seeded via <a href="https://docs.rs/getrandom"><code>getrandom</code></a>.</p> |
| <p>This method is the recommended way to construct non-deterministic PRNGs |
| since it is convenient and secure.</p> |
| <p>In case the overhead of using <a href="https://docs.rs/getrandom"><code>getrandom</code></a> to seed <em>many</em> PRNGs is an |
| issue, one may prefer to seed from a local PRNG, e.g. |
| <code>from_rng(thread_rng()).unwrap()</code>.</p> |
| <h5 id="panics"><a href="#panics">Panics</a></h5> |
| <p>If <a href="https://docs.rs/getrandom"><code>getrandom</code></a> is unable to provide secure entropy this method will panic.</p> |
| </div></details></div><h2 id="implementors" class="small-section-header">Implementors<a href="#implementors" class="anchor"></a></h2><div id="implementors-list"><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-SeedableRng-for-BlockRng64%3CR%3E" class="impl has-srclink"><a class="srclink rightside" href="../src/rand_core/block.rs.html#412-429">source</a><a href="#impl-SeedableRng-for-BlockRng64%3CR%3E" class="anchor"></a><h3 class="code-header">impl<R: <a class="trait" href="block/trait.BlockRngCore.html" title="trait rand_core::block::BlockRngCore">BlockRngCore</a> + <a class="trait" href="trait.SeedableRng.html" title="trait rand_core::SeedableRng">SeedableRng</a>> <a class="trait" href="trait.SeedableRng.html" title="trait rand_core::SeedableRng">SeedableRng</a> for <a class="struct" href="block/struct.BlockRng64.html" title="struct rand_core::block::BlockRng64">BlockRng64</a><R></h3></section></summary><div class="impl-items"><section id="associatedtype.Seed-1" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Seed-1" class="anchor"></a><h4 class="code-header">type <a href="#associatedtype.Seed" class="associatedtype">Seed</a> = <R as <a class="trait" href="trait.SeedableRng.html" title="trait rand_core::SeedableRng">SeedableRng</a>>::<a class="associatedtype" href="trait.SeedableRng.html#associatedtype.Seed" title="type rand_core::SeedableRng::Seed">Seed</a></h4></section></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-SeedableRng-for-BlockRng%3CR%3E" class="impl has-srclink"><a class="srclink rightside" href="../src/rand_core/block.rs.html#243-260">source</a><a href="#impl-SeedableRng-for-BlockRng%3CR%3E" class="anchor"></a><h3 class="code-header">impl<R: <a class="trait" href="block/trait.BlockRngCore.html" title="trait rand_core::block::BlockRngCore">BlockRngCore</a> + <a class="trait" href="trait.SeedableRng.html" title="trait rand_core::SeedableRng">SeedableRng</a>> <a class="trait" href="trait.SeedableRng.html" title="trait rand_core::SeedableRng">SeedableRng</a> for <a class="struct" href="block/struct.BlockRng.html" title="struct rand_core::block::BlockRng">BlockRng</a><R></h3></section></summary><div class="impl-items"><section id="associatedtype.Seed-2" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Seed-2" class="anchor"></a><h4 class="code-header">type <a href="#associatedtype.Seed" class="associatedtype">Seed</a> = <R as <a class="trait" href="trait.SeedableRng.html" title="trait rand_core::SeedableRng">SeedableRng</a>>::<a class="associatedtype" href="trait.SeedableRng.html#associatedtype.Seed" title="type rand_core::SeedableRng::Seed">Seed</a></h4></section></div></details></div><script src="../implementors/rand_core/trait.SeedableRng.js" async></script></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="rand_core" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
