New issue from Damien Lebrun-Grandie: "Missing Mandates clauses on is_sufficiently_aligned"

Author: Dani-Hub

xml/issue4290.xml

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+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="4290" status="New">
+<title>Missing <i>Mandates</i> clauses on `is_sufficiently_aligned`</title>
+<section>
+<sref ref="[ptr.align]"/>
+</section>
+<submitter>Damien Lebrun-Grandie</submitter>
+<date>03 Jul 2025</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+`is_sufficiently_aligned` should mandate that the alignment template argument is a power of two 
+and that it is greater equal to the byte alignment of its type template argument.
+<p/>
+In <sref ref="[ptr.align]"/> `is_sufficiently_aligned` has no <i>Mandates</i> element. It is an 
+oversight that we realized when implementing <paper num="P2897R7"/> into libc++ 
+(in <a href="https://github.com/llvm/llvm-project/pull/122603">https://github.com/llvm/llvm-project/pull/122603</a>). 
+The function template was originally proposed as a static member function of the `aligned_accessor` 
+class template which has these two <i>Mandates</i> clauses and therefore applied 
+(see <sref ref="[mdspan.accessor.aligned.overview]"/> p1). It revision <paper num="P2897R4"/>, 
+`is_sufficiently_aligned` was moved out the class template definition to become the free function
+ memory helper that was voted into C++26 but the <i>Mandates</i> were lost in the process.
+<p/>
+We propose to correct that oversight and reintroduce the following <i>Mandates</i> clauses right above 
+<sref ref="[ptr.align]"/> p10.
+</p>
+</discussion>
+
+<resolution>
+<p>
+This wording is relative to <paper num="N5008"/>.
+</p>
+
+<ol>
+
+<li><p>Modify <sref ref="[ptr.align]"/> as indicated:</p>
+
+<blockquote>
+<pre>
+template&lt;size_t Alignment, class T&gt;
+  bool is_sufficiently_aligned(T* ptr);
+</pre>
+<blockquote>
+<p>
+<ins>-?- <i>Mandates</i>:</ins>
+</p>
+<ol style="list-style-type: none">
+<li><p><ins>(?.1) &mdash; `Alignment` is a power of two, and</ins></p></li>
+<li><p><ins>(?.2) &mdash; <tt>Alignment &gt;= alignof(T)</tt> is `true`.</ins></p></li>
+</ol>
+<p>
+-10- <i>Preconditions</i>: `p` points to an object `X` of a type similar 
+(<sref ref="[conv.qual]"/>) to `T`.
+<p/>
+-11- <i>Returns</i>: `true` if `X` has alignment at least `Alignment`, otherwise `false`.
+<p/>
+-12- <i>Throws</i>: Nothing.
+</p>
+</blockquote>
+</blockquote>
+</li>
+
+</ol>
+</resolution>
+
+</issue>