Class StructureWithBitfields

pythonmemorymodule/pefile.py:1422–1527

Extends Structure's functionality with support for bitfields such as: ('B:4,LowerHalf', 'B:4,UpperHalf') To this end, two lists are maintained: * self.__keys__ that contains compound fields, for example ('B,~LowerHalfUpperHalf'), and is used during packing/unpaking

class StructureWithBitfields(Structure):
    """
    Extends Structure's functionality with support for bitfields such as:
        ('B:4,LowerHalf', 'B:4,UpperHalf')
    To this end, two lists are maintained:
        * self.__keys__ that contains compound fields, for example
          ('B,~LowerHalfUpperHalf'), and is used during packing/unpaking
        * self.__keys_ext__ containing a separate key for each field (ex., LowerHalf,
          UpperHalf) to simplify implementation of dump()
    This way the implementation of unpacking/packing and dump() from Structure can be
    reused.

    In addition, we create a dictionary:
        <comound_field_index_in_keys> -->
            (data type, [ (subfield name, length in bits)+ ] )
    that facilitates bitfield paking and unpacking.

    With lru_cache() creating only once instance per format string, the memory
    overhead is negligible.
    """

    BTF_NAME_IDX = 0
    BTF_BITCNT_IDX = 1
    CF_TYPE_IDX = 0
    CF_SUBFLD_IDX = 1

    def __init__(self, format, name=None, file_offset=None):
        (
            self.__format__,
            self.__format_length__,
            self.__field_offsets__,
            self.__keys__,
            self.__keys_ext__,
            self.__compound_fields__,
        ) = set_bitfields_format(format)
        # create our own unpacked_data_elms to ensure they are not shared among
        # StructureWithBitfields instances with the same format string
        self.__unpacked_data_elms__ = [None for i in range(self.__format_length__)]
        self.__all_zeroes__ = False
        self.__file_offset__ = file_offset
        self.name = name if name != None else format[0]

    def __unpack__(self, data):
        # calling the original routine to deal with special cases/spurious data
        # structures
        super(StructureWithBitfields, self).__unpack__(data)
        self._unpack_bitfield_attributes()

    def __pack__(self):
        self._pack_bitfield_attributes()
        try:
            data = super(StructureWithBitfields, self).__pack__()
        finally:
            self._unpack_bitfield_attributes()
        return data

    def dump(self, indentation=0):
        tk = self.__keys__