USHORT
CmpCompressedNameSize(
  IN  PWCHAR Name,
  IN  ULONG Length
  );

Routine Description:

    Computes the length of the unicode string that the given compressed name
    expands into.

Arguments:

    Name - Supplies the compressed name.

    Length - Supplies the length in bytes of the compressed name

Return Value:

    The number of bytes of storage required to hold the Unicode expanded name.