#!/usr/bin/env python
#
# RunLength decoder (Adobe version) implementation based on PDF Reference
# version 1.4 section 3.3.4.
#
#  * public domain *
#

def rldecode(data):
    """
    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.
    >>> s = "\x05123456\xfa7\x04abcde\x80junk"
    >>> rldecode(s)
    '1234567777777abcde'
    """
    decoded = []
    i = 0
    while i < len(data):
        #print "data[%d]=:%d:" % (i,ord(data[i]))
        length = ord(data[i])
        if length == 128:
            break
        if length >= 0 and length < 128:
            run = data[i+1:(i+1)+(length+1)]
            #print "length=%d, run=%s" % (length+1,run)
            decoded.append(run)
            i = (i+1) + (length+1)
        if length > 128:
            run = data[i+1]*(257-length)
            #print "length=%d, run=%s" % (257-length,run)
            decoded.append(run)
            i = (i+1) + 1
    return ''.join(decoded)


if __name__ == '__main__':
    import doctest
    doctest.testmod()
