BOOLEAN
RtlEqualPrefixSid(
  IN  PSID Sid1,
  IN  PSID Sid2
  );

Routine Description:

    This procedure tests two SID prefix values for equality.

    An SID prefix is the entire SID except for the last sub-authority
    value.

Arguments:

    Sid1, Sid2 - Supply pointers to the two SID values to compare.
        The SID structures are assumed to be valid.

Return Value:

    BOOLEAN - TRUE if the prefix value of Sid1 is equal to Sid2, and FALSE
        otherwise.