ULONG
RtlFindClearBits(
  IN  PRTL_BITMAP BitMapHeader,
  IN  ULONG NumberToFind,
  IN  ULONG HintIndex
  );

Routine Description:

    This procedure searches the specified bit map for the specified
    contiguous region of clear bits.  If a run is not found from the
    hint to the end of the bitmap, we will search again from the
    beginning of the bitmap.

Arguments:

    BitMapHeader - Supplies a pointer to the previously initialized BitMap.

    NumberToFind - Supplies the size of the contiguous region to find.

    HintIndex - Supplies the index (zero based) of where we should start
        the search from within the bitmap.

Return Value:

    ULONG - Receives the starting index (zero based) of the contiguous
        region of clear bits found.  If not such a region cannot be found
        a -1 (i.e. 0xffffffff) is returned.