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112 lines
4.6 KiB
HTML
112 lines
4.6 KiB
HTML
<article id="wikiArticle">
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<div></div>
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<h2 id="Summary" name="Summary">概述</h2>
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<p><code><strong>Math.clz32() </strong></code>函数返回一个数字在转换成 32 无符号整形数字的二进制形式后, 开头的 0 的个数, 比如 <code>1000000</code> 转换成 32 位无符号整形数字的二进制形式后是 <code>00000000000011110100001001000000</code>, 开头的 0 的个数是 12 个, 则 <code>Math.clz32(1000000)</code> 返回 <code>12</code>.</p>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript"><code>Math.clz32 (x)
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</code></code></pre>
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<h3 id="Parameters" name="Parameters">参数</h3>
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<dl>
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<dt>x</dt>
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<dd>一个数字.</dd>
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</dl>
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<h2 id="描述" style="line-height: 30px;">描述</h2>
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<p>"clz32" 是 CountLeadingZeroes32 的缩写.</p>
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<p>如果 <code>x</code> 不是数字类型, 则它首先会被转换成数字类型, 然后再转成 32 位无符号整形数字. </p>
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<p>如果转换后的 32 位无符号整形数字是 <code>0</code>, 则返回 <code>32</code>, 因为此时所有位上都是 <code>0</code>.</p>
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<p><code>NaN</code>, <code>Infinity</code>,<code> -Infinity</code> 这三个数字转成 32 位无符号整形数字后都是 <code>0</code>.</p>
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<p><span>这个函数主要用于那些编译目标为 JS 语言的系统中, 比如 Emscripten.</span></p>
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<h2 id="示例">示例</h2>
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<pre><code class="language-javascript">Math.clz32(1) // 31
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Math.clz32(1000) // 22
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Math.clz32() // 32
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[NaN, Infinity, -Infinity, 0, -0, null, undefined, "foo", {}, []].filter(function (n) {
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return Math.clz32(n) !== 32
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}) // []
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Math.clz32(true) // 31
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Math.clz32(3.5) // 30
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</code></pre>
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<h2 id="Compatibility" name="Compatibility">Polyfill</h2>
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<pre><code class="language-javascript">Math.clz32 = Math.clz32 || function(value) {
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var value = Number(value) >>> 0;
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return value ? 32 - value.toString(2).length : 32;
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}
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</code></pre>
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<h2 id="规范">规范</h2>
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<table class="standard-table">
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<tbody>
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<tr>
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<th scope="col">Specification</th>
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<th scope="col">Status</th>
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<th scope="col">Comment</th>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-Math.clz32" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.clz32</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td>Initial definition.</td>
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</tr>
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</tbody>
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</table>
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<h2 id="浏览器兼容性">浏览器兼容性</h2>
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<div><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
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This compatibility table still uses the old format,
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because we haven't yet converted the data it contains.
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<strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
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<div class="htab">
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<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
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<ul>
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<li class="selected"><a>Desktop</a></li>
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<li><a>Mobile</a></li>
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</ul>
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</div></div>
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<div id="compat-desktop">
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<table class="compat-table">
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<tbody>
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<tr>
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<th>Feature</th>
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<th>Chrome</th>
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<th>Firefox (Gecko)</th>
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<th>Internet Explorer</th>
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<th>Opera</th>
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<th>Safari</th>
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</tr>
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<tr>
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<td>Basic support</td>
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<td>35</td>
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<td><a href="/en-US/Firefox/Releases/31" title="Released on 2014-07-22.">31</a> (31)</td>
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<td><span style="color: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</span></td>
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</tr>
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</tbody>
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</table>
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</div>
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<div id="compat-mobile">
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<table class="compat-table">
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<tbody>
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<tr>
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<th>Feature</th>
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<th>Android</th>
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<th>Chrome for Android</th>
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<th>Firefox Mobile (Gecko)</th>
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<th>IE Mobile</th>
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<th>Opera Mobile</th>
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<th>Safari Mobile</th>
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</tr>
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<tr>
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<td>Basic support</td>
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<td><span style="color: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</span></td>
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<td>31.0 (31)</td>
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<td><span style="color: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</span></td>
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<td><span style="color: #f00;">未实现</span></td>
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</tr>
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</tbody>
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</table>
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</div>
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<h2 id="See_also" name="See_also">相关链接</h2>
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<ul>
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<li><a href="Reference/Global_Objects/Math" title="Math 是一个内置对象， 它具有数学常数和函数的属性和方法。不是一个函数对象。"><code>Math</code></a></li>
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</ul>
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</article> |