Math.clz32()

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

The following polyfill is the most efficient.

if (!Math.clz32) {
  Math.clz32 = 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 - Math.floor(Math.log(x >>> 0) * Math.LOG2E);
  };
}

Specifications

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.
Draft  

Browser compatibility

FeatureChromeFirefoxEdgeInternet ExplorerOperaSafari
Basic Support3831(Yes)(No)25(Yes)
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support(Yes)(Yes)(Yes)31(No)(Yes)(Yes)

See also

Document Tags and Contributors

 Last updated by: fscholz,