How can I test for negative zero?

Initially I thought Math.Sign would be the proper way to go but after running a test it seems that it treats -0.0 and +0.0 the same.

Solution 1:

Here's a grotty hack way of doing it:

private static readonly long NegativeZeroBits =
    BitConverter.DoubleToInt64Bits(-0.0);

public static bool IsNegativeZero(double x)
{
    return BitConverter.DoubleToInt64Bits(x) == NegativeZeroBits;
}

Basically that's testing for the exact bit pattern of -0.0, but without having to hardcode it.

Solution 2:

After a bit of searching I finally made it to Section 7.7.2 of the C# specification and came up with this solution.

private static bool IsNegativeZero(double x)
{
    return x == 0.0 && double.IsNegativeInfinity(1.0 / x);
}