PHP strange result of multiplying by -1

Question

$res = 0.0 * -1.0;

I get float -0

What is this strange behavior?

Answer 1

Floating point numbers allow have a signed zero.

You shouldn't worry, however, as +0.0 === -0.0 ^(demo). (Not that you should use that sort of comparison for floats.)

Answer 2

Because floating-point has both +0 and -0.