def process(self, data):
dst = bytearray()
src = StructReader(data)
while not src.eof:
copy = src.read_byte()
for mask in (0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80):
if src.eof:
break
if not copy & mask:
dst.append(src.read_byte())
continue
elif not dst:
raise ValueError('copy requested against empty buffer')
with src.be:
match_len = src.read_integer(6) + _MATCH_MIN
match_pos = src.read_integer(10)
if not match_pos or match_pos > len(dst):
raise RuntimeError(F'invalid match offset at position {src.tell()}')
match_pos = len(dst) - match_pos
while match_len > 0:
match = dst[match_pos:match_pos + match_len]
dst.extend(match)
match_pos += len(match)
match_len -= len(match)
return dst
def test_bitreader_le(self):
data = 0b10010100111010100100001111101_11_00000000_0101010101010010010111100000101001010101100000001110010111110100_111_000_100
size, remainder = divmod(data.bit_length(), 8)
self.assertEqual(remainder, 0)
data = memoryview(data.to_bytes(size, 'little'))
sr = StructReader(data)
self.assertEqual(sr.read_integer(3), 0b100)
self.assertEqual(sr.read_integer(3), 0b000)
self.assertEqual(sr.read_integer(3), 0b111)
self.assertEqual(
sr.u64(),
0b0101010101010010010111100000101001010101100000001110010111110100)
self.assertFalse(any(sr.read_flags(8, reverse=True)))
self.assertEqual(sr.read_bit(), 1)
self.assertRaises(ValueError, lambda: sr.read_struct(''))
self.assertEqual(sr.read_bit(), 1)
self.assertEqual(sr.read_integer(29), 0b10010100111010100100001111101)
self.assertTrue(sr.eof)
def test_bitreader_be(self):
data = 0b01010_10011101_0100100001_1111_0111101010000101010101010010010111100000101001010101100000001110010111110100111000_101
size, remainder = divmod(data.bit_length(), 8)
self.assertEqual(remainder, 7)
data = memoryview(data.to_bytes(size + 1, 'big'))
sr = StructReader(data)
with sr.be:
self.assertEqual(sr.read_bit(), 0)
self.assertEqual(sr.read_bit(), 1)
self.assertEqual(sr.read_bit(), 0)
self.assertEqual(sr.read_bit(), 1)
self.assertEqual(sr.read_bit(), 0)
self.assertEqual(sr.read_byte(), 0b10011101)
self.assertEqual(sr.read_integer(10), 0b100100001)
self.assertTrue(all(sr.read_flags(4)))
self.assertEqual(
sr.read_integer(82),
0b0111101010000101010101010010010111100000101001010101100000001110010111110100111000
)
self.assertRaises(EOF, sr.u16)
def _decompress_xpress_huffman(self,
reader: StructReader,
writer: MemoryFile,
target: Optional[int] = None,
max_chunk_size: int = 0x10000) -> None:
limit = writer.tell()
if target is not None:
target += limit
while not reader.eof:
if reader.remaining_bytes < XPRESS_NUM_SYMBOLS // 2:
raise IndexError(
F'There are only {reader.remaining_bytes} bytes reamining in the input buffer,'
F' but at least {XPRESS_NUM_SYMBOLS//2} are required to read a Huffman table.'
)
table = bytearray(
reader.read_integer(4) for _ in range(XPRESS_NUM_SYMBOLS))
table = make_huffman_decode_table(table, XPRESS_TABLEBITS,
XPRESS_MAX_CODEWORD_LEN)
limit = limit + max_chunk_size
flags = BitBufferedReader(reader, 16)
while True:
position = writer.tell()
if position == target:
if reader.remaining_bytes:
self.log_info(
F'chunk decompressed with {reader.remaining_bytes} bytes remaining in input buffer'
)
return
if position >= limit:
if position > limit:
limit = position
self.log_info(
F'decompression of one chunk generated more than the limit of {max_chunk_size} bytes'
)
flags.collect()
break
try:
sym = flags.huffman_symbol(table, XPRESS_TABLEBITS,
XPRESS_MAX_CODEWORD_LEN)
except EOFError:
self.log_debug('end of file while reading huffman symbol')
break
if sym < XPRESS_NUM_CHARS:
writer.write_byte(sym)
continue
length = sym & 0xF
offsetlog = (sym >> 4) & 0xF
flags.collect()
if reader.eof:
break
offset = (1 << offsetlog) | flags.read(offsetlog)
if length == 0xF:
nudge = reader.read_byte()
if nudge < 0xFF:
length += nudge
else:
length = reader.u16() or reader.u32()
length += XPRESS_MIN_MATCH_LEN
writer.replay(offset, length)
