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- #!/usr/bin/env python3
-
- """ Python implementation of ASCII85/ASCIIHex decoder (Adobe version).
-
- This code is in the public domain.
-
- """
-
- import re
- import struct
-
- def ascii85decode(data):
- """
- In ASCII85 encoding, every four bytes are encoded with five ASCII
- letters, using 85 different types of characters (as 256**4 < 85**5).
- When the length of the original bytes is not a multiple of 4, a special
- rule is used for round up.
-
- The Adobe's ASCII85 implementation is slightly different from
- its original in handling the last characters.
-
- The sample string is taken from:
- http://en.wikipedia.org/w/index.php?title=Ascii85
- """
- if isinstance(data, str):
- data = data.encode('ascii')
- n = b = 0
- out = bytearray()
- for c in data:
- if ord('!') <= c and c <= ord('u'):
- n += 1
- b = b*85+(c-33)
- if n == 5:
- out += struct.pack(b'>L',b)
- n = b = 0
- elif c == ord('z'):
- assert n == 0
- out += b'\0\0\0\0'
- elif c == ord('~'):
- if n:
- for _ in range(5-n):
- b = b*85+84
- out += struct.pack(b'>L',b)[:n-1]
- break
- return bytes(out)
-
- hex_re = re.compile(r'([a-f\d]{2})', re.IGNORECASE)
- trail_re = re.compile(r'^(?:[a-f\d]{2}|\s)*([a-f\d])[\s>]*$', re.IGNORECASE)
- def asciihexdecode(data):
- """
- ASCIIHexDecode filter: PDFReference v1.4 section 3.3.1
- For each pair of ASCII hexadecimal digits (0-9 and A-F or a-f), the
- ASCIIHexDecode filter produces one byte of binary data. All white-space
- characters are ignored. A right angle bracket character (>) indicates
- EOD. Any other characters will cause an error. If the filter encounters
- the EOD marker after reading an odd number of hexadecimal digits, it
- will behave as if a 0 followed the last digit.
- """
- decode = (lambda hx: chr(int(hx, 16)))
- out = list(map(decode, hex_re.findall(data)))
- m = trail_re.search(data)
- if m:
- out.append(decode("%c0" % m.group(1)))
- return ''.join(out)
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