private void MappedValues()
{ // mode 1
Debug.Assert(_mappedLength == Math.Min(_readerDataValues.Length, _mappedDataValues.Length), "incorrect precomputed length");
int length = _mappedLength;
for (int i = 0; i < length; ++i)
{
_mappedDataValues[i] = _readerDataValues[i]; // from reader to dataset
};
}