41 lines
1.3 KiB
Python
41 lines
1.3 KiB
Python
|
#
|
||
|
# 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
|