45 lines
1.5 KiB
Python
45 lines
1.5 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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import six #Python 2+3 compatibility
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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 = b''
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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 = six.indexbytes(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+=six.int2byte(six.indexbytes(data,j))
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#print 'length=%d, run=%s' % (length+1,run)
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i = (i+1) + (length+1)
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if length > 128:
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run = six.int2byte(six.indexbytes(data,i+1))*(257-length)
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#print 'length=%d, run=%s' % (257-length,run)
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decoded+=run
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i = (i+1) + 1
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return decoded
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