Comments on: Double bitwise NOT (~~)

By: Art

Art — Mon, 07 Feb 2011 19:08:39 +0000

I meant not going to work. (typo)

By: Art

Art — Mon, 07 Feb 2011 19:08:01 +0000

~~ is going to work as Math.floor for negative numbers.

~~(-2.999) = -2
Math.floor(-2.999) = -3

By: Mathias Bynens

Mathias Bynens — Sun, 01 Aug 2010 09:09:43 +0000

Note that bitwise operators convert numbers to a 32-bit sequence before processing them, so the range is different. Alternatives to Math.floor using bitwise operators will only work with positive signed 32-bit floats, i.e. numbers from 0 to +2,147,483,647 (2^31-1).

~~2147483647.1; // 2147483647
~~2147483648.1; // -2147483648

I’ve created a jsPerf test case to benchmark these different approaches. Feel free to add more possibilities!

By: Tom

Tom — Mon, 19 Apr 2010 12:29:23 +0000

Or you could add 0.5 and have Math.round() and by adding 1 you’d have Math.ceil();

Math.floor(x) == ~~(x)
Math.round(x) == ~~(x + 0.5)
Math.ceil(x) == ~~(x + 1)

Cheers,
Tom

By: Martin Kirk

Martin Kirk — Fri, 16 Apr 2010 08:39:41 +0000

@Carlos

ahhh — yes you are right !

By: Carlos

Carlos — Fri, 16 Apr 2010 08:35:30 +0000

@Martin Kirk My question remains, shouldn’t this line

var SelectedOptions = Option3 & Option6 & Option10; //= 1000100100

var SelectedOptions = Option3 | Option6 | Option10; //= 1000100100

By: Martin Kirk

Martin Kirk — Fri, 16 Apr 2010 07:44:37 +0000

@Carlos

sorry… the HTML formatting has been fixed

By: Martin Kirk

Martin Kirk — Fri, 16 Apr 2010 07:36:38 +0000

@Carlos

what’s up with the & ???
the bitwise operator is ‘&’

By: SJL Web Design

SJL Web Design — Thu, 15 Apr 2010 19:12:01 +0000

Great article, thanks to Martin for his additional pieces of code too.

By: carlos

carlos — Thu, 25 Mar 2010 16:04:10 +0000

Shouldn’t @Martin Kirk example be:

var Option1 = 2
var Option2 = 4
var Option3 = 8
var Option4 = 16
var Option10 = 1024
 
var SelectedOptions = Option3 | Option6 | Option10; //= 1000100100
 
if(Option6 &amp; SelectedOptions) {
    doSomething()
}