| 1234567891011121314151617181920212223242526272829303132333435363738 |
- #
- # RunLength decoder (Adobe version) implementation based on PDF Reference
- # version 1.4 section 3.3.4.
- #
- # * public domain *
- #
- from typing import List
- def rldecode(data: bytes) -> bytes:
- """RunLength decoder (Adobe version) implementation based on PDF Reference
- version 1.4 section 3.3.4:
- The RunLengthDecode filter decodes data that has been encoded in a
- simple byte-oriented format based on run length. The encoded data
- is a sequence of runs, where each run consists of a length byte
- followed by 1 to 128 bytes of data. If the length byte is in the
- range 0 to 127, the following length + 1 (1 to 128) bytes are
- copied literally during decompression. If length is in the range
- 129 to 255, the following single byte is to be copied 257 - length
- (2 to 128) times during decompression. A length value of 128
- denotes EOD.
- """
- decoded_array: List[int] = []
- data_iter = iter(data)
- while True:
- length = next(data_iter, 128)
- if length == 128:
- break
- if 0 <= length < 128:
- decoded_array.extend((next(data_iter) for _ in range(length + 1)))
- if length > 128:
- run = [next(data_iter)] * (257 - length)
- decoded_array.extend(run)
- return bytes(decoded_array)
|
