mirror of
https://github.com/TheAlgorithms/Python.git
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882fb2f3c9
* rewrite of base85.py * changed maps to list comprehension * Apply suggestions from code review Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com> --------- Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>
59 lines
1.8 KiB
Python
59 lines
1.8 KiB
Python
"""
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Base85 (Ascii85) encoding and decoding
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https://en.wikipedia.org/wiki/Ascii85
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"""
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def _base10_to_85(d: int) -> str:
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return "".join(chr(d % 85 + 33)) + _base10_to_85(d // 85) if d > 0 else ""
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def _base85_to_10(digits: list) -> int:
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return sum(char * 85**i for i, char in enumerate(reversed(digits)))
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def ascii85_encode(data: bytes) -> bytes:
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"""
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>>> ascii85_encode(b"")
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b''
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>>> ascii85_encode(b"12345")
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b'0etOA2#'
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>>> ascii85_encode(b"base 85")
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b'@UX=h+?24'
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"""
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binary_data = "".join(bin(ord(d))[2:].zfill(8) for d in data.decode("utf-8"))
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null_values = (32 * ((len(binary_data) // 32) + 1) - len(binary_data)) // 8
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binary_data = binary_data.ljust(32 * ((len(binary_data) // 32) + 1), "0")
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b85_chunks = [int(_s, 2) for _s in map("".join, zip(*[iter(binary_data)] * 32))]
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result = "".join(_base10_to_85(chunk)[::-1] for chunk in b85_chunks)
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return bytes(result[:-null_values] if null_values % 4 != 0 else result, "utf-8")
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def ascii85_decode(data: bytes) -> bytes:
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"""
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>>> ascii85_decode(b"")
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b''
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>>> ascii85_decode(b"0etOA2#")
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b'12345'
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>>> ascii85_decode(b"@UX=h+?24")
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b'base 85'
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"""
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null_values = 5 * ((len(data) // 5) + 1) - len(data)
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binary_data = data.decode("utf-8") + "u" * null_values
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b85_chunks = map("".join, zip(*[iter(binary_data)] * 5))
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b85_segments = [[ord(_s) - 33 for _s in chunk] for chunk in b85_chunks]
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results = [bin(_base85_to_10(chunk))[2::].zfill(32) for chunk in b85_segments]
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char_chunks = [
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[chr(int(_s, 2)) for _s in map("".join, zip(*[iter(r)] * 8))] for r in results
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]
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result = "".join("".join(char) for char in char_chunks)
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offset = int(null_values % 5 == 0)
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return bytes(result[: offset - null_values], "utf-8")
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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