How to use the gitdb.stream.DecompressMemMapReader function in gitdb

delta_offset = (delta_offset << 7) + (c & 0x7f)
        # END character loop
        delta_info = delta_offset
        total_rela_offset = i
    # REF DELTA
    elif type_id == REF_DELTA:
        total_rela_offset = data_rela_offset + 20
        delta_info = data[data_rela_offset:total_rela_offset]
    # BASE OBJECT
    else:
        # assume its a base object
        total_rela_offset = data_rela_offset
    # END handle type id
    abs_data_offset = offset + total_rela_offset
    if as_stream:
        stream = DecompressMemMapReader(buffer(data, total_rela_offset), False, uncomp_size)
        if delta_info is None:
            return abs_data_offset, OPackStream(offset, type_id, uncomp_size, stream)
        else:
            return abs_data_offset, ODeltaPackStream(offset, type_id, uncomp_size, delta_info, stream)
    else:
        if delta_info is None:
            return abs_data_offset, OPackInfo(offset, type_id, uncomp_size)
        else:
            return abs_data_offset, ODeltaPackInfo(offset, type_id, uncomp_size, delta_info)
        # END handle info

delta_offset = (delta_offset << 7) + (c & 0x7f)
        # END character loop
        delta_info = delta_offset
        total_rela_offset = i
    # REF DELTA
    elif type_id == REF_DELTA:
        total_rela_offset = data_rela_offset + 20
        delta_info = data[data_rela_offset:total_rela_offset]
    # BASE OBJECT
    else:
        # assume its a base object
        total_rela_offset = data_rela_offset
    # END handle type id
    abs_data_offset = offset + total_rela_offset
    if as_stream:
        stream = DecompressMemMapReader(buffer(data, total_rela_offset), False, uncomp_size)
        if delta_info is None:
            return abs_data_offset, OPackStream(offset, type_id, uncomp_size, stream)
        else:
            return abs_data_offset, ODeltaPackStream(offset, type_id, uncomp_size, delta_info, stream)
    else:
        if delta_info is None:
            return abs_data_offset, OPackInfo(offset, type_id, uncomp_size)
        else:
            return abs_data_offset, ODeltaPackInfo(offset, type_id, uncomp_size, delta_info)
        # END handle info

def new(self, m, close_on_deletion=False):
        """Create a new DecompressMemMapReader instance for acting as a read-only stream
        This method parses the object header from m and returns the parsed
        type and size, as well as the created stream instance.

        :param m: memory map on which to operate. It must be object data ( header + contents )
        :param close_on_deletion: if True, the memory map will be closed once we are
            being deleted"""
        inst = DecompressMemMapReader(m, close_on_deletion, 0)
        typ, size = inst._parse_header_info()
        return typ, size, inst