strict rules,    x + 0.0 becomes x:    False
strict rules,    x + (-0.0) becomes x: True
fast math rules, x + 0.0 becomes x:    True
x = -0.0, the program gives 0.0 with sign 1.0
the unsafe rule would give   -0.0 with sign -1.0
1 / +0.0 = inf   1 / -0.0 = -inf
