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最終更新日時(UTC):
<span itemprop="datePublished" content="2025-07-08T15:33:39">
2025年07月08日 15時33分39秒
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<span itemprop="author" itemscope itemtype="http://schema.org/Person">
<span itemprop="name">Akira Takahashi</span>
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<div class="identifier-type">function template</div><div class="header"><numeric></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">mul_sat</span><span class="cpp cpp26" title="C++26で追加">(C++26)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">mul_sat</span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">y</span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>飽和乗算 <code>x * y</code> を計算する。</p>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Constraints。関数であればオーバーロード解決に参加するための条件、それ以外であれば受け付ける型の条件">テンプレートパラメータ制約</a></h2>
<p><code>T</code>は符号付き整数型または符号無し整数型であること。</p>
<h2><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a></h2>
<ul>
<li>無限の範囲で計算した値<code>x * y</code>が型<code>T</code>で表現可能ならば、<code>x * y</code>を返す</li>
<li>そうでないとき、型<code>T</code>で表現可能な最大値または最小値のうち<code>x * y</code>に近い方の値を返す</li>
</ul>
<h2><a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a></h2>
<p>投げない</p>
<h2>例</h2>
<p><div class="yata" id="f85a88e295ec6e7491e9e7ac9348cfc0d650588c"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../cstdint.html"><cstdint></a></span>
<span class="cp">#include <a href="../numeric.html"><numeric></a></span>
<span class="cp">#include <a href="../print.html"><print></a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// 2 * 3 = 6</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::mul_sat</span></span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">));</span>
<span class="w"> </span><span class="c1">// 20 * 20 = 400 -> 255(2**8-1)</span>
<span class="w"> </span><span class="n"><a href="../cstdint/uint8_t.html">std::uint8_t</a></span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">20</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::mul_sat</span></span><span class="p">(</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">));</span>
<span class="w"> </span><span class="c1">// -128 * -1 = 128 -> 127(2**7-1)</span>
<span class="w"> </span><span class="n"><a href="../cstdint/int8_t.html">std::int8_t</a></span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">-128</span><span class="p">,</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">-1</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::mul_sat</span></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">y</span><span class="p">));</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>6
255
127
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++26</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: ??</li>
<li><a href="../../implementation.html#gcc">GCC</a>: ??</li>
<li><a href="../../implementation.html#icc">ICC</a>: ??</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p0543r3.html" target="_blank">P0543R3 Saturation arithmetic</a></li>
</ul></div>
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