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c#.netfloating-pointdouble

Calculate the unit in the last place (ULP) for doubles

Does .NET have a built-in method to calculate the ULP of a given double or float?

If not, what is the most efficient way to do so?

Solution

  • It seems the function is pretty trivial; this is based on the pseudocode in the accepted answer to the question linked by vulkanino:

    double value = whatever;
long bits = BitConverter.DoubleToInt64Bits(value);
double nextValue = BitConverter.Int64BitsToDouble(bits + 1);
double result = nextValue - value;

    For floats, you'd need to provide your own implementation of SingleToInt32Bits and Int32BitsToSingle, since BitConverter doesn't have those functions.

    This page shows the special cases in the java implementation of the function; handling those should be fairly trivial, too.