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42 lines
1.5 KiB
42 lines
1.5 KiB
#!/usr/bin/env python3
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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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import sys
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def rldecode(data):
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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 = []
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i=0
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while i < len(data):
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#print "data[%d]=:%d:" % (i,ord(data[i]))
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length = ord(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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run = data[i+1:(i+1)+(length+1)]
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#print "length=%d, run=%s" % (length+1,run)
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decoded.append(run)
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i = (i+1) + (length+1)
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if length > 128:
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run = data[i+1]*(257-length)
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#print "length=%d, run=%s" % (257-length,run)
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decoded.append(run)
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i = (i+1) + 1
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return ''.join(decoded)
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