Using bitwise OR 0 to floor a number

javascript floating-point bit-manipulation

2022-08-30 00:52:36

A colleague of mine stumbled upon a method to floor float numbers using a bitwise or:

var a = 13.6 | 0; //a == 13

We were talking about it and wondering a few things.

How does it work? Our theory was that using such an operator casts the number to an integer, thus removing the fractional part
Does it have any advantages over doing ? Maybe it's a bit faster? (pun not intended)Math.floor
Does it have any disadvantages? Maybe it doesn't work in some cases? Clarity is an obvious one, since we had to figure it out, and well, I'm writting this question.

Thanks.

答案 1

How does it work? Our theory was that using such an operator casts the number to an integer, thus removing the fractional part

All bitwise operations except unsigned right shift, , work on signed 32-bit integers. So using bitwise operations will convert a float to an integer.>>>

Does it have any advantages over doing Math.floor? Maybe it's a bit faster? (pun not intended)

http://jsperf.com/or-vs-floor/2 seems slightly faster

Does it have any disadvantages? Maybe it doesn't work in some cases? Clarity is an obvious one, since we had to figure it out, and well, I'm writting this question.

Will not pass jsLint.
32-bit signed integers only
Odd Comparative behavior: , while Math.floor(NaN) === NaN(NaN | 0) === 0

答案 2

This is truncation as opposed to flooring. Howard's answer is sort of correct; But I would add that does exactly what it is supposed to with respect to negative numbers. Mathematically, that is what a floor is. Math.floor

In the case you described above, the programmer was more interested in truncation or chopping the decimal completely off. Although, the syntax they used sort of obscures the fact that they are converting the float to an int.