~30

[Otto Deckelman]

I believe the symbol is called a tilda, but correct me if I'm wrong. What does this mean and represent in computer math? Art M. replied to my question yesterday about bitwise shift operators and used this in his explanation.

[Nathan Pruett]

Otto -
Yes, this symbol is called a tilde, and it is the bitwise inversion operator. Basically what it does is switch all the bit values of an integer value from 0 to 1 and from 1 to 0...
so :

 15 = 0000 0000 0000 0000 0000 0000 0000 1111
~15 = 1111 1111 1111 1111 1111 1111 1111 0000
-16 = 1111 1111 1111 1111 1111 1111 1111 0000
 30 = 0000 0000 0000 0000 0000 0000 0001 1110
~30 = 1111 1111 1111 1111 1111 1111 1110 0001
-31 = 1111 1111 1111 1111 1111 1111 1110 0001

So the bitwise inversion of 15 = -16 and the bitwise inversion of 30 = -31...
Does this make sense?
HTH,
-Nate
[This message has been edited by Nathan Pruett (edited April 06, 2001).]

[Otto Deckelman]

thanks, it helps alot.