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