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<section id="sfc64-small-fast-chaotic-prng">
<h1>SFC64 Small Fast Chaotic PRNG<a class="headerlink" href="#sfc64-small-fast-chaotic-prng" title="Link to this heading">#</a></h1>
<dl class="py class">
<dt class="sig sig-object py" id="numpy.random.SFC64">
<em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">numpy.random.</span></span><span class="sig-name descname"><span class="pre">SFC64</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">seed</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#numpy.random.SFC64" title="Link to this definition">#</a></dt>
<dd><p>BitGenerator for Chris Doty-Humphrey’s Small Fast Chaotic PRNG.</p>
<dl class="field-list simple">
<dt class="field-odd">Parameters<span class="colon">:</span></dt>
<dd class="field-odd"><dl class="simple">
<dt><strong>seed</strong><span class="classifier">{None, int, array_like[ints], SeedSequence}, optional</span></dt><dd><p>A seed to initialize the <a class="reference internal" href="generated/numpy.random.BitGenerator.html#numpy.random.BitGenerator" title="numpy.random.BitGenerator"><code class="xref py py-obj docutils literal notranslate"><span class="pre">BitGenerator</span></code></a>. If None, then fresh,
unpredictable entropy will be pulled from the OS. If an <code class="docutils literal notranslate"><span class="pre">int</span></code> or
<code class="docutils literal notranslate"><span class="pre">array_like[ints]</span></code> is passed, then it will be passed to
<a class="reference internal" href="generated/numpy.random.SeedSequence.html#numpy.random.SeedSequence" title="numpy.random.SeedSequence"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SeedSequence</span></code></a> to derive the initial <a class="reference internal" href="generated/numpy.random.BitGenerator.html#numpy.random.BitGenerator" title="numpy.random.BitGenerator"><code class="xref py py-obj docutils literal notranslate"><span class="pre">BitGenerator</span></code></a> state. One may also
pass in a <a class="reference internal" href="generated/numpy.random.SeedSequence.html#numpy.random.SeedSequence" title="numpy.random.SeedSequence"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SeedSequence</span></code></a> instance.</p>
</dd>
</dl>
</dd>
</dl>
<p class="rubric">Notes</p>
<p><a class="reference internal" href="#numpy.random.SFC64" title="numpy.random.SFC64"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SFC64</span></code></a> is a 256-bit implementation of Chris Doty-Humphrey’s Small Fast
Chaotic PRNG (<a class="reference internal" href="#r50352647a6aa-1" id="id1">[1]</a>). <a class="reference internal" href="#numpy.random.SFC64" title="numpy.random.SFC64"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SFC64</span></code></a> has a few different cycles that one might be
on, depending on the seed; the expected period will be about
<span class="math notranslate nohighlight">\(2^{255}\)</span> (<a class="reference internal" href="#r50352647a6aa-2" id="id2">[2]</a>). <a class="reference internal" href="#numpy.random.SFC64" title="numpy.random.SFC64"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SFC64</span></code></a> incorporates a 64-bit counter which means
that the absolute minimum cycle length is <span class="math notranslate nohighlight">\(2^{64}\)</span> and that distinct
seeds will not run into each other for at least <span class="math notranslate nohighlight">\(2^{64}\)</span> iterations.</p>
<p><a class="reference internal" href="#numpy.random.SFC64" title="numpy.random.SFC64"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SFC64</span></code></a> provides a capsule containing function pointers that produce
doubles, and unsigned 32 and 64- bit integers. These are not
directly consumable in Python and must be consumed by a <a class="reference internal" href="../generator.html#numpy.random.Generator" title="numpy.random.Generator"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Generator</span></code></a>
or similar object that supports low-level access.</p>
<p><strong>State and Seeding</strong></p>
<p>The <a class="reference internal" href="#numpy.random.SFC64" title="numpy.random.SFC64"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SFC64</span></code></a> state vector consists of 4 unsigned 64-bit values. The last
is a 64-bit counter that increments by 1 each iteration.</p>
<p>The input seed is processed by <a class="reference internal" href="generated/numpy.random.SeedSequence.html#numpy.random.SeedSequence" title="numpy.random.SeedSequence"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SeedSequence</span></code></a> to generate the first
3 values, then the <a class="reference internal" href="#numpy.random.SFC64" title="numpy.random.SFC64"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SFC64</span></code></a> algorithm is iterated a small number of times
to mix.</p>
<p><strong>Compatibility Guarantee</strong></p>
<p><a class="reference internal" href="#numpy.random.SFC64" title="numpy.random.SFC64"><code class="xref py py-obj docutils literal notranslate"><span class="pre">SFC64</span></code></a> makes a guarantee that a fixed seed will always produce the same
random integer stream.</p>
<p class="rubric">References</p>
<div role="list" class="citation-list">
<div class="citation" id="r50352647a6aa-1" role="doc-biblioentry">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id1">1</a><span class="fn-bracket">]</span></span>
<p><a class="reference external" href="https://pracrand.sourceforge.net/RNG_engines.txt">“PractRand”</a></p>
</div>
<div class="citation" id="r50352647a6aa-2" role="doc-biblioentry">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id2">2</a><span class="fn-bracket">]</span></span>
<p><a class="reference external" href="https://www.pcg-random.org/posts/random-invertible-mapping-statistics.html">“Random Invertible Mapping Statistics”</a></p>
</div>
</div>
</dd></dl>
<section id="state">
<h2>State<a class="headerlink" href="#state" title="Link to this heading">#</a></h2>
<div class="pst-scrollable-table-container"><table class="autosummary longtable table autosummary">
<tbody>
<tr class="row-odd"><td><p><a class="reference internal" href="generated/numpy.random.SFC64.state.html#numpy.random.SFC64.state" title="numpy.random.SFC64.state"><code class="xref py py-obj docutils literal notranslate"><span class="pre">state</span></code></a></p></td>
<td><p>Get or set the PRNG state</p></td>
</tr>
</tbody>
</table>
</div>
</section>
<section id="extending">
<h2>Extending<a class="headerlink" href="#extending" title="Link to this heading">#</a></h2>
<div class="pst-scrollable-table-container"><table class="autosummary longtable table autosummary">
<tbody>
<tr class="row-odd"><td><p><a class="reference internal" href="generated/numpy.random.SFC64.cffi.html#numpy.random.SFC64.cffi" title="numpy.random.SFC64.cffi"><code class="xref py py-obj docutils literal notranslate"><span class="pre">cffi</span></code></a></p></td>
<td><p>CFFI interface</p></td>
</tr>
<tr class="row-even"><td><p><a class="reference internal" href="generated/numpy.random.SFC64.ctypes.html#numpy.random.SFC64.ctypes" title="numpy.random.SFC64.ctypes"><code class="xref py py-obj docutils literal notranslate"><span class="pre">ctypes</span></code></a></p></td>
<td><p>ctypes interface</p></td>
</tr>
</tbody>
</table>
</div>
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