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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>bit_floor</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-numeric.html">numeric</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-bit.html">&lt;bit&gt;</a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> T <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> T bit_floor<span class="br0">(</span>T x<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<p>&#33509; <code>x</code> &#38750;&#38646;&#65292;&#21017;&#35745;&#31639;&#19981;&#22823;&#20110; <code>x</code> &#30340;&#26368;&#22823;&#30340;&#20108;&#30340;&#25972;&#25968;&#27425;&#24130;&#12290;&#33509; <code>x</code> &#20026;&#38646;&#65292;&#21017;&#36820;&#22238;&#38646;&#12290;</p>
<p>&#27492;&#37325;&#36733;&#20165;&#33509; <code>T</code> &#20026;&#26080;&#31526;&#21495;&#25972;&#25968;&#31867;&#22411;&#65288;&#21363; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> &#12289; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">short</span></span></span> &#12289; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span> &#12289; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span></span></span> &#12289; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span></span></span> &#25110;&#25193;&#23637;&#26080;&#31526;&#21495;&#25972;&#25968;&#31867;&#22411;&#65289;&#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</p>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#33509; <code>x</code> &#20026;&#38646;&#21017;&#20026;&#38646;&#65307;&#21542;&#21017;&#20026;&#19981;&#22823;&#20110; <code>x</code> &#30340;&#26368;&#22823;&#30340;&#20108;&#30340;&#25972;&#25968;&#27425;&#24130;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">&#21487;&#33021;&#30340;&#23454;&#29616;</span></h3>
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<pre class="de1"><span class="kw1">template</span> <span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">unsigned_integral</span> T<span class="sy1">&gt;</span>
requires <span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1">&lt;</span>T, <span class="kw4">bool</span><span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span> <span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1">&lt;</span>T, <span class="kw4">char</span><span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span>
<span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1">&lt;</span>T, char8_t<span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span> <span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1">&lt;</span>T, <span class="kw4">char16_t</span><span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span>
<span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1">&lt;</span>T, <span class="kw4">char32_t</span><span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span> <span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1">&lt;</span>T, <span class="kw4">wchar_t</span><span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> T bit_floor<span class="br0">(</span>T x<span class="br0">)</span> <span class="kw1">noexcept</span>
<span class="br0">{</span>
<span class="kw1">if</span> <span class="br0">(</span>x <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span>
<span class="kw1">return</span> T<span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>std<span class="sy4">::</span><span class="me2">bit_width</span><span class="br0">(</span>x<span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<pre class="de1"><span class="co2">#include &lt;bit&gt;</span>
<span class="co2">#include &lt;bitset&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="kw4">auto</span> main<span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> <span class="kw4">int</span>
<span class="br0">{</span>
<span class="kw1">using</span> bin <span class="sy1">=</span> <a href="cpp-utility-bitset.html"><span class="kw1027">std::<span class="me2">bitset</span></span></a><span class="sy1">&lt;</span><span class="nu0">8</span><span class="sy1">&gt;</span><span class="sy4">;</span>
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">unsigned</span> x <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> x <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">10</span><span class="sy4">;</span> <span class="sy2">++</span>x<span class="br0">)</span>
<span class="br0">{</span>
<span class="kw4">auto</span> <span class="kw4">const</span> z <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">bit_floor</span><span class="br0">(</span>x<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// P1956R1 &#21069;&#20026; `floor2`</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;bit_floor(&quot;</span> <span class="sy1">&lt;&lt;</span> bin<span class="br0">(</span>x<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;) = &quot;</span> <span class="sy1">&lt;&lt;</span> bin<span class="br0">(</span>z<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">bit_floor(00000000) = 00000000
bit_floor(00000001) = 00000001
bit_floor(00000010) = 00000010
bit_floor(00000011) = 00000010
bit_floor(00000100) = 00000100
bit_floor(00000101) = 00000100
bit_floor(00000110) = 00000100
bit_floor(00000111) = 00000100
bit_floor(00001000) = 00001000
bit_floor(00001001) = 00001000</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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<div><a href="cpp-numeric-bit_ceil.html"><span class="t-lines"><span>bit_ceil</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#23547;&#25214;&#19981;&#23567;&#20110;&#32473;&#23450;&#20540;&#30340;&#26368;&#23567;&#30340;&#20108;&#30340;&#25972;&#25968;&#27425;&#24130;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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<div><a href="cpp-numeric-rotr.html"><span class="t-lines"><span>rotr</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#35745;&#31639;&#36880;&#20301;&#21491;&#26059;&#36716;&#30340;&#32467;&#26524;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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<div><a href="cpp-numeric-bit_width.html"><span class="t-lines"><span>bit_width</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#23547;&#25214;&#34920;&#31034;&#32473;&#23450;&#20540;&#25152;&#38656;&#30340;&#26368;&#23567;&#20301;&#25968;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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<div><a href="cpp-numeric-has_single_bit.html"><span class="t-lines"><span>has_single_bit</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#26816;&#26597;&#19968;&#20010;&#25968;&#26159;&#21542;&#20026;&#20108;&#30340;&#25972;&#25968;&#27425;&#24130;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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