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37 lines
1.0 KiB
Python
37 lines
1.0 KiB
Python
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"""
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The Fletcher checksum is an algorithm for computing a position-dependent
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checksum devised by John G. Fletcher (1934–2012) at Lawrence Livermore Labs
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in the late 1970s.[1] The objective of the Fletcher checksum was to
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provide error-detection properties approaching those of a cyclic
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redundancy check but with the lower computational effort associated
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with summation techniques.
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Source: https://en.wikipedia.org/wiki/Fletcher%27s_checksum
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"""
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def fletcher16(text: str) -> int:
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"""
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Loop through every character in the data and add to two sums.
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>>> fletcher16('hello world')
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6752
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>>> fletcher16('onethousandfourhundredthirtyfour')
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28347
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>>> fletcher16('The quick brown fox jumps over the lazy dog.')
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5655
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"""
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data = bytes(text, "ascii")
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sum1 = 0
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sum2 = 0
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for character in data:
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sum1 = (sum1 + character) % 255
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sum2 = (sum1 + sum2) % 255
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return (sum2 << 8) | sum1
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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