#1,092 – Positive and Negative Zero

Because .NET uses the IEEE 754 standard to represent floating point numbers, it allows representing both positive and negative zero values.  (+0.0 and -0.0).

Mathematically, +0.0 is equal to -0.0 and an equality check in C# will return a true result.  However, although the values are considered equal, either value can be represented in C# and they are stored differently in memory.

            float zero = 0.0f;
            float negZero = -0.0f;

            bool theyAreEqual = zero == negZero;   // true

            // 00-00-00-00
            Console.WriteLine(BitConverter.ToString(BitConverter.GetBytes(zero)));

            // 00-00-00-80
            Console.WriteLine(BitConverter.ToString(BitConverter.GetBytes(negZero)));

            float sum1 = zero + 1.0f;
            float sum2 = negZero + 1.0f;
            bool sumsEqual = sum1 == sum2;    // true

1092-001

 

You can think of  a floating point representation of zero as being either zero or a very small positive number that rounds to zero when stored as a floating point.  If the value was a tiny bit above zero before rounding, it’s stored as +0.0.  If it was a bit below zero before rounding, it’s stored as -0.0.

Advertisements

About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: