What's the function of the ~ bitwise operator (Tilde)

php operators bit-manipulation tilde
Michiel picture Michiel · Feb 3, 2012 · Viewed 25k times · Source

Possible Duplicate:
What does this ~ operator mean here?
Bit not operation in PHP(or any other language probably)

Can someone explain me the ~ operator in PHP? I know it's a NOT-operator, but why does PHP convert following statement to the negative value of the variable minus one?

$a = 1; echo ~$a    // echo -2
$a = 2; echo ~$a    // echo -3
$a = 3; echo ~$a    // echo -4

Answer

buc picture buc · Feb 3, 2012

This is called the two's complement arithmetic. You can read about it in more detail here.

The operator ~ is a binary negation operator (as opposed to boolean negation), and being that, it inverses all the bits of its operand. The result is a negative number in two's complement arithmetic.

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