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The Math.clz32()
function returns the number of leading zero bits in the 32-bit binary representation of a number.
Syntax
Math.clz32(x)
Parameters
x
- A number.
Return value
The number of leading zero bits in the 32-bit binary representation of the given number.
Description
"clz32
" is short for CountLeadingZeroes32
.
If x
is not a number, then it will be converted to a number first, then converted to a 32-bit unsigned integer.
If the converted 32-bit unsigned integer is 0
, then return 32
, because all bits are 0
.
This function is particularly useful for systems that compile to JS, like Emscripten.
Examples
Using Math.clz32()
Math.clz32(1); // 31 Math.clz32(1000); // 22 Math.clz32(); // 32 [NaN, Infinity, -Infinity, 0, -0, null, undefined, 'foo', {}, []].filter( function(n) { return Math.clz32(n) !== 32 }); // [] Math.clz32(true); // 31 Math.clz32(3.5); // 30
Polyfill
This polyfill depends on Math.imul
.
Math.clz32 = Math.clz32 || (function () { 'use strict'; var table = [ 32, 31, 0, 16, 0, 30, 3, 0, 15, 0, 0, 0, 29, 10, 2, 0, 0, 0, 12, 14, 21, 0, 19, 0, 0, 28, 0, 25, 0, 9, 1, 0, 17, 0, 4, , 0, 0, 11, 0, 13, 22, 20, 0, 26, 0, 0, 18, 5, 0, 0, 23, 0, 27, 0, 6, 0, 24, 7, 0, 8, 0, 0, 0] // Adapted from an algorithm in Hacker's Delight, page 103. return function (x) { // Note that the variables may not necessarily be the same. // 1. Let n = ToUint32(x). var v = Number(x) >>> 0 // 2. Let p be the number of leading zero bits in the 32-bit binary representation of n. v |= v >>> 1 v |= v >>> 2 v |= v >>> 4 v |= v >>> 8 v |= v >>> 16 v = table[Math.imul(v, 0x06EB14F9) >>> 26] // Return p. return v } })();
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Math.clz32' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Math.clz32' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 38 | 31 (31) | No support | 25 | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | No support | 31.0 (31) | No support | No support | No support |
See also
Document Tags and Contributors
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