The Math.clz32() function returns the number of leading zero bits in the 32-bit binary representation of a number.




A number.

Return value

The number of leading zero bits in the 32-bit binary representation of the given number.


"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.


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


The following polyfill is the most efficient.

if (!Math.clz32) Math.clz32 = (function(log, LN2){
  return function(x) {
    // Let n be ToUint32(x).
    // Let p be the number of leading zero bits in 
    // the 32-bit binary representation of n.
    // Return p.    
    if (x == null || x === 0) {
      return 32;
    return 31 - log(x >>> 0) / LN2 | 0; // the "| 0" acts like math.floor
})(Math.log, Math.LN2);


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Math.clz32' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Math.clz32' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Basic supportChrome Full support 38Edge Full support YesFirefox Full support 31IE No support NoOpera Full support 25Safari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 31Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 0.12


Full support  
Full support
No support  
No support

See also

Document Tags and Contributors

Last updated by: mfuji09,