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<title>Issue 4224: Philox engines should be freestanding</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#WP">WP</a> status.</em></p>
<h3 id="4224"><a href="lwg-defects.html#4224">4224</a>. Philox engines should be freestanding</h3>
<p><b>Section:</b> 29.5.4.5 <a href="https://wg21.link/rand.eng.philox">[rand.eng.philox]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Jiang An <b>Opened:</b> 2025-03-15 <b>Last modified:</b> 2025-06-23</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#rand.eng.philox">issues</a> in [rand.eng.philox].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Philox engines don't seem to require floating-point operations or support from the operating system, 
so they are probably suitable for freestanding. However, as <a href="https://wg21.link/P2976R1" title=" Freestanding Library: algorithm, numeric, and random">P2976R1</a> was finished before 
the adoption of <a href="https://wg21.link/P2075R6" title=" Philox as an extension of the C++ RNG engines">P2075R6</a>, these engines are not made freestanding yet.
</p>

<p><i>[2025-06-13; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after ten votes in favour during reflector poll.
</p>

<p><i>[Sofia 2025-06-21; Status changed: Voting &rarr; WP.]</i></p>



<p id="res-4224"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N5001" title=" Working Draft, Programming Languages — C++">N5001</a>.
</p>

<ol>

<li><p>Modify 29.5.2 <a href="https://wg21.link/rand.synopsis">[rand.synopsis]</a>, header <code>&lt;random&gt;</code> synopsis, as indicated:</p>

<blockquote>
<pre>
[&hellip;]
// <i>29.5.4.5 <a href="https://wg21.link/rand.eng.philox">[rand.eng.philox]</a>, class template philox_engine</i>
template&lt;class UIntType, size_t w, size_t n, size_t r, UIntType... consts&gt;
  class philox_engine;               <ins>// <i>partially freestanding</i></ins>

[&hellip;]
using philox4x32 = <i>see below</i>; <ins>// <i>freestanding</i></ins>
using philox4x64 = <i>see below</i>; <ins>// <i>freestanding</i></ins>
[&hellip;]
</pre>
</blockquote>
</li>

<li><p>Modify 29.5.4.5 <a href="https://wg21.link/rand.eng.philox">[rand.eng.philox]</a>, class template <code class='backtick'>philox_engine</code> synopsis, as indicated:</p>

<blockquote>
<pre>
namespace std {
  template&lt;class UIntType, size_t w, size_t n, size_t r, UIntType... consts&gt;
  class philox_engine {
    [&hellip;]  
    // <i>inserters and extractors</i>
    template&lt;class charT, class traits&gt;
      friend basic_ostream&lt;charT, traits&gt;&amp;
        operator&lt;&lt;(basic_ostream&lt;charT, traits&gt;&amp; os, const philox_engine&amp; x); <ins>// <i>hosted</i></ins>
    template&lt;class charT, class traits&gt;
      friend basic_istream&lt;charT, traits&gt;&amp;
        operator&gt;&gt;(basic_istream&lt;charT, traits&gt;&amp; is, philox_engine&amp; x);       <ins>// <i>hosted</i></ins>
  };
}
</pre>
</blockquote>
</li>
</ol>





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