public void Test_EncodedBitFieldDescriptor_CalculateRequiredBitFieldSize()
{
// Test case where all values are null (expected 0 bits of entropy)
EncodedBitFieldDescriptor descriptor = new EncodedBitFieldDescriptor()
{
AllValuesAreNull = true,
};
descriptor.CalculateRequiredBitFieldSize();
Assert.Equal(0, descriptor.RequiredBits);
// Test case where there is 1024 possible values plus an encoded null value, resulting in 10 required bits
descriptor = new EncodedBitFieldDescriptor()
{
AllValuesAreNull = false,
EncodedNullValue = 1023,
MinValue = 0,
MaxValue = 1023,
};
descriptor.CalculateRequiredBitFieldSize();
Assert.Equal(10, descriptor.RequiredBits);
// Test case where there is 1024 possible values plus an encoded null value, resulting in 11 required bits
descriptor = new EncodedBitFieldDescriptor()
{
AllValuesAreNull = false,
EncodedNullValue = 1024,
MinValue = 0,
MaxValue = 1024,
};
descriptor.CalculateRequiredBitFieldSize();
Assert.Equal(11, descriptor.RequiredBits);
}
// CalculateAttributeValueRange scans a single attribute across all records in a block of values
public static void CalculateAttributeValueRange(long[] Values,
int startIndex, int count,
long Mask,
long ANativeNullValue, bool ANullable,
ref EncodedBitFieldDescriptor FieldDescriptor)
{
bool ObservedANullValue = false;
bool FirstValue = true;
FieldDescriptor.NativeNullValue = ANativeNullValue;
FieldDescriptor.MinValue = ANativeNullValue;
FieldDescriptor.MaxValue = ANativeNullValue;
FieldDescriptor.Nullable = ANullable;
for (int i = startIndex, limit = startIndex + count; i < limit; i++)
{
long TestValue = Values[i];
// Ensure negative values are preserved
TestValue = TestValue < 0 ? -(-TestValue & Mask) : TestValue & Mask;
if (FieldDescriptor.Nullable)
{
if (FieldDescriptor.MinValue == ANativeNullValue || (TestValue != ANativeNullValue && TestValue < FieldDescriptor.MinValue))
{
FieldDescriptor.MinValue = TestValue;
}
if (FieldDescriptor.MaxValue == ANativeNullValue || (TestValue != ANativeNullValue && TestValue > FieldDescriptor.MaxValue))
{
FieldDescriptor.MaxValue = TestValue;
}
}
else
{
if (FirstValue || TestValue < FieldDescriptor.MinValue)
{
FieldDescriptor.MinValue = TestValue;
}
if (FirstValue || TestValue > FieldDescriptor.MaxValue)
{
FieldDescriptor.MaxValue = TestValue;
}
}
if (!ObservedANullValue && ANullable && TestValue == ANativeNullValue)
{
ObservedANullValue = true;
}
FirstValue = false;
}
// If the data stream processed contained no null values, then force the
// nullable flag to false so we don't encode an extra token for a null value
// that will never be written.
if (!ObservedANullValue)
{
FieldDescriptor.Nullable = false;
}
if (FieldDescriptor.Nullable && FieldDescriptor.MaxValue != FieldDescriptor.NativeNullValue)
{
FieldDescriptor.MaxValue++;
FieldDescriptor.EncodedNullValue = FieldDescriptor.MaxValue;
}
else
{
FieldDescriptor.EncodedNullValue = 0;
}
FieldDescriptor.CalculateRequiredBitFieldSize();
}