Can I turn negative number to positive with bitwise operations in Actionscript 3?

Question

Is there a direct way how to turn a negative number to positive using bitwise operations in Actionscript 3? I just think I've read somewhere that it is possible and faster than using Math.abs() or multiplying by -1. Or am I wrong and it was a dream after day long learning about bytes and bitwise operations?

What I saw was that bitwise NOT almost does the trick:

// outputs: 449
trace( ~(-450) );

If anyone find this question and is interested - in 5 million iterations ~(x) + 1 is 50% faster than Math.abs(x).

Answer 1

You need to add one after taking the bitwise negation. This is a property of two's complement number system. It is not related to Actionscript (aside from the alleged performance difference).

So, (~(-450)+1) gives 450
and (~(450)+1) gives -450.

As noted in comments, this answer is written in response to the question, to fix a minor issue in the question asker's experiment. This answer is not an endorsement of this technique for general software development use.

Answer 2

Use the rule that says

~(x) = (-x)-1

Answer 3

If two-complement is being used (usually the case), negation is complement then add 1:

-x == ~x + 1

Whether it's faster depends on what optimisations the compiler performs. When in doubt, test.