# JavaScript Faster multiplication or division by powers of 2

## Example

Shifting bits left (right) is equivalent to multiplying (dividing) by 2. It's the same in base 10: if we "left-shift" `13` by `2` places, we get `1300`, or `13 * (10 ** 2)`. And if we take `12345` and "right-shift" by `3` places and then remove the decimal part, we get `12`, or `Math.floor(12345 / (10 ** 3))`. So if we want to multiply a variable by `2 ** n`, we can just left-shift by `n` bits.

``````console.log(13 * (2 ** 6)) //13 * 64 = 832
console.log(13    <<   6)  //          832
``````

Similarly, to do (floored) integer division by `2 ** n`, we can right shift by `n` bits. Example:

``````console.log(1000 / (2 ** 4)) //1000 / 16 = 62.5
console.log(1000    >>   4)  //            62
``````

It even works with negative numbers:

``````console.log(-80 / (2 ** 3)) //-80 / 8 = -10
console.log(-80      >> 3)  //          -10
``````

In reality, speed of arithmetic is unlikely to significantly impact how long your code takes to run, unless you are doing on the order of 100s of millions of computations. But C programmers love this sort of thing! PDF - Download JavaScript for free