41 lines
1.3 KiB
Python
41 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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def rldecode(data: bytes) -> bytes:
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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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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 = b""
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i = 0
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while i < len(data):
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length = data[i]
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if length == 128:
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break
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if length >= 0 and length < 128:
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for j in range(i + 1, (i + 1) + (length + 1)):
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decoded += bytes((data[j],))
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i = (i + 1) + (length + 1)
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if length > 128:
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run = bytes((data[i + 1],)) * (257 - length)
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decoded += run
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i = (i + 1) + 1
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return decoded
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