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Running
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#
# RunLength decoder (Adobe version) implementation based on PDF Reference
# version 1.4 section 3.3.4.
#
# * public domain *
#
def rldecode(data: bytes) -> bytes:
"""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.
"""
decoded = b""
i = 0
while i < len(data):
length = data[i]
if length == 128:
break
if length >= 0 and length < 128:
for j in range(i + 1, (i + 1) + (length + 1)):
decoded += bytes((data[j],))
i = (i + 1) + (length + 1)
if length > 128:
run = bytes((data[i + 1],)) * (257 - length)
decoded += run
i = (i + 1) + 1
return decoded
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