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Add decompression support for 'dcmp' (1)-compressed resources
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dgelessus
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acd056973e
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@ -28,7 +28,7 @@ STRUCT_COMPRESSED_HEADER = struct.Struct(">4sHHI")
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# 2 bytes: Reserved (always zero).
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STRUCT_COMPRESSED_APPLICATION_HEADER = struct.Struct(">BBhH")
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# Lookup table for codes in range(0x4b, 0xfe) in "application" compressed resources.
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# Lookup table for codes in range(0x4b, 0xfe) in 'dcmp' (0)-compressed resources.
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# This table was obtained by decompressing a manually created compressed resource that refers to every possible table entry. Detailed steps:
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# 1. Create a file with a resource fork
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# 2. Add a resource with the following contents: b'\xa8\x9fer\x00\x12\x08\x01\x00\x00\x01f\x80\x03\x00\x00\x00\x00' + bytes(range(0x4b, 0xfe)) + b'\xff'
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@ -36,7 +36,7 @@ STRUCT_COMPRESSED_APPLICATION_HEADER = struct.Struct(">BBhH")
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# 4. Open the file in ResEdit
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# 5. Duplicate the resource - this will decompress the original resource and write its contents uncompressed into the duplicate
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# 6. Read the data from the duplicated resource
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COMPRESSED_APPLICATION_TABLE_DATA = (
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COMPRESSED_APPLICATION_0_TABLE_DATA = (
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# First line corresponds to codes in range(0x4b, 0x50).
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b"\x00\x00N\xba\x00\x08Nu\x00\x0c"
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# All following lines correspond to 8 codes each.
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@ -65,8 +65,31 @@ COMPRESSED_APPLICATION_TABLE_DATA = (
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b"\x04\x80\x00h\x0b|D\x00A\xe8HA"
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)
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# Note: index 0 in this table corresponds to code 0x4b, index 1 to 0x4c, etc.
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COMPRESSED_APPLICATION_TABLE = [COMPRESSED_APPLICATION_TABLE_DATA[i:i + 2] for i in range(0, len(COMPRESSED_APPLICATION_TABLE_DATA), 2)]
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assert len(COMPRESSED_APPLICATION_TABLE) == len(range(0x4b, 0xfe))
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COMPRESSED_APPLICATION_0_TABLE = [COMPRESSED_APPLICATION_0_TABLE_DATA[i:i + 2] for i in range(0, len(COMPRESSED_APPLICATION_0_TABLE_DATA), 2)]
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assert len(COMPRESSED_APPLICATION_0_TABLE) == len(range(0x4b, 0xfe))
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# Lookup table for codes in range(0xd5, 0xfe) in 'dcmp' (1)-compressed resources.
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# This table was obtained by decompressing a manually created compressed resource that refers to every possible table entry. Detailed steps:
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# 1. Create a file with a resource fork
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# 2. Add a resource with the following contents: b'\xa8\x9fer\x00\x12\x08\x01\x00\x00\x00R\x80\x03\x00\x01\x00\x00' + bytes(range(0xd5, 0xfe)) + b'\xff'
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# 3. Set the "compressed" flag (0x01) on the resource
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# 4. Open the file in ResEdit
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# 5. Duplicate the resource - this will decompress the original resource and write its contents uncompressed into the duplicate
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# 6. Read the data from the duplicated resource
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COMPRESSED_APPLICATION_1_TABLE_DATA = (
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# First line corresponds to codes in range(0xd5, 0xd8).
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b"\x00\x00\x00\x01\x00\x02"
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# All following lines correspond to 8 codes each.
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b"\x00\x03.\x01>\x01\x01\x01\x1e\x01\xff\xff\x0e\x011\x00"
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b"\x11\x12\x01\x0732\x129\xed\x10\x01'#\"\x017"
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b"\x07\x06\x01\x17\x01#\x00\xff\x00/\x07\x0e\xfd<\x015"
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b"\x01\x15\x01\x02\x00\x07\x00>\x05\xd5\x02\x01\x06\x07\x07\x08"
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# Last line corresponds to codes in range(0xf8, 0xfe).
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b"0\x01\x013\x00\x10\x17\x167>67"
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)
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# Note: index 0 in this table corresponds to code 0xd5, index 1 to 0xd6, etc.
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COMPRESSED_APPLICATION_1_TABLE = [COMPRESSED_APPLICATION_1_TABLE_DATA[i:i + 2] for i in range(0, len(COMPRESSED_APPLICATION_1_TABLE_DATA), 2)]
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assert len(COMPRESSED_APPLICATION_1_TABLE) == len(range(0xd5, 0xfe))
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# Header continuation part for a "system" compressed resource.
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# 2 bytes: The ID of the 'dcmp' resource that can decompress this resource. Currently only ID 2 is supported.
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@ -237,7 +260,7 @@ def _decompress_application_0(data: bytes, decompressed_length: int, *, debug: b
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i += 1
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if debug:
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print(f"Fixed table reference to 0x{table_index:>02x}")
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entry = COMPRESSED_APPLICATION_TABLE[table_index]
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entry = COMPRESSED_APPLICATION_0_TABLE[table_index]
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if debug:
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print(f"\t-> {entry}")
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decompressed += entry
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@ -421,7 +444,133 @@ def _decompress_application_0(data: bytes, decompressed_length: int, *, debug: b
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def _decompress_application_1(data: bytes, decompressed_length: int, *, debug: bool=False) -> bytes:
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raise NotImplementedError("'dcmp' (1) decompression not supported yet")
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prev_literals = []
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decompressed = b""
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i = 0
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while i < len(data):
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byte = data[i]
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if debug:
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print(f"Tag byte 0x{byte:>02x}, at 0x{i:x}, decompressing to 0x{len(decompressed):x}")
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if byte in range(0x00, 0x20):
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# Literal byte sequence, 1-byte header.
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# The length of the literal data is stored in the low nibble of the tag byte.
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count = (byte >> 0 & 0xf) + 1
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begin = i + 1
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end = begin + count
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# Controls whether or not the literal is stored so that it can be referenced again later.
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do_store = byte >= 0x10
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literal = data[begin:end]
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if debug:
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print(f"Literal (1-byte header, storing: {do_store})")
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print(f"\t-> {literal}")
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decompressed += literal
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if do_store:
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if debug:
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print(f"\t-> stored as literal number 0x{len(prev_literals):x}")
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prev_literals.append(literal)
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i = end
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elif byte in range(0x20, 0xd0):
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# Backreference to a previous literal, 1-byte form.
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# This can reference literals with indices in range(0xb0).
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table_index = byte - 0x20
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i += 1
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if debug:
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print(f"Backreference (1-byte form) to 0x{table_index:>02x}")
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literal = prev_literals[table_index]
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if debug:
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print(f"\t-> {literal}")
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decompressed += literal
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elif byte in (0xd0, 0xd1):
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# Literal byte sequence, 2-byte header.
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# The length of the literal data is stored in the following byte.
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count = data[i+1]
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begin = i + 2
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end = begin + count
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# Controls whether or not the literal is stored so that it can be referenced again later.
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do_store = byte == 0xd1
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literal = data[begin:end]
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if debug:
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print(f"Literal (2-byte header, storing: {do_store})")
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print(f"\t-> {literal}")
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decompressed += literal
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if do_store:
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if debug:
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print(f"\t-> stored as literal number 0x{len(prev_literals):x}")
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prev_literals.append(literal)
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i = end
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elif byte == 0xd2:
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# Backreference to a previous literal, 2-byte form.
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# This can reference literals with indices in range(0xb0, 0x1b0).
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table_index = data[i+1] + 0xb0
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i += 2
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if debug:
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print(f"Backreference (2-byte form) to 0x{table_index:>02x}")
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literal = prev_literals[table_index]
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if debug:
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print(f"\t-> {literal}")
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decompressed += literal
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elif byte in range(0xd5, 0xfe):
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# Reference into a fixed table of two-byte literals.
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# All compressed resources use the same table.
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table_index = byte - 0xd5
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i += 1
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if debug:
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print(f"Fixed table reference to 0x{table_index:>02x}")
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entry = COMPRESSED_APPLICATION_1_TABLE[table_index]
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if debug:
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print(f"\t-> {entry}")
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decompressed += entry
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elif byte == 0xfe:
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# Extended code, whose meaning is controlled by the following byte.
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i += 1
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kind = data[i]
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if debug:
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print(f"Extended code: 0x{kind:>02x}")
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i += 1
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if kind == 0x02:
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# Repeat 1 byte a certain number of times.
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byte_count = 1 # Unlike with 'dcmp' (0) compression, there doesn't appear to be a 2-byte repeat (or if there is, it's never used in practice).
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if debug:
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print(f"Repeat {byte_count}-byte value")
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# The byte(s) to repeat, stored as a variable-length integer. The value is treated as unsigned, i. e. the integer is never negative.
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to_repeat_int, length = _read_variable_length_integer(data, i)
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i += length
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try:
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to_repeat = to_repeat_int.to_bytes(byte_count, "big", signed=False)
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except OverflowError:
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raise DecompressError(f"Value to repeat out of range for {byte_count}-byte repeat: {to_repeat_int:#x}")
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count_m1, length = _read_variable_length_integer(data, i)
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i += length
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count = count_m1 + 1
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if count <= 0:
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raise DecompressError(f"Repeat count must be positive: {count}")
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repeated = to_repeat * count
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if debug:
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print(f"\t-> {to_repeat} * {count}: {repeated}")
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decompressed += repeated
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else:
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raise DecompressError(f"Unknown extended code: 0x{kind:>02x}")
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elif byte == 0xff:
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# End of data marker, always occurs exactly once as the last byte of the compressed data.
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if debug:
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print("End marker")
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if i != len(data) - 1:
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raise DecompressError(f"End marker reached at {i}, before the expected end of data at {len(data) - 1}")
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i += 1
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else:
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raise DecompressError(f"Unknown tag byte: 0x{data[i]:>02x}")
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return decompressed
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def _decompress_application(data: bytes, decompressed_length: int, *, debug: bool=False) -> bytes:
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