Math.imul

The Math.imul() function returns the result of the C-like 32-bit multiplication of the two parameters.

Syntax

Math.imul(a, b)

Parameters

a

First number.

b

Second number.

Return value

The result of the C-like 32-bit multiplication of the given arguments.

Description

Math.imul() allows for fast 32-bit integer multiplication with C-like semantics. This feature is useful for projects like Emscripten. Because imul() is a static method of Math, you always use it as Math.imul(), rather than as a method of a Math object you created (Math is not a constructor).

Examples

Using Math.imul()

Math.imul(2, 4);          // 8
Math.imul(-1, 8);         // -8
Math.imul(-2, -2);        // 4
Math.imul(0xffffffff, 5); // -5
Math.imul(0xfffffffe, 5); // -10

Polyfill

This can be emulated with the following function:

Math.imul = Math.imul || function(a, b) {
  var ah = (a >>> 16) & 0xffff;
  var al = a & 0xffff;
  var bh = (b >>> 16) & 0xffff;
  var bl = b & 0xffff;
  // the shift by 0 fixes the sign on the high part
  // the final |0 converts the unsigned value into a signed value
  return ((al * bl) + (((ah * bl + al * bh) << 16) >>> 0)|0);
};

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Math.imul' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of 'Math.imul' in that specification.	Draft

Browser compatibility