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40 lines
1.3 KiB
Python
40 lines
1.3 KiB
Python
"""
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This algorithm was created for sdbm (a public-domain reimplementation of ndbm)
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database library.
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It was found to do well in scrambling bits, causing better distribution of the keys
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and fewer splits.
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It also happens to be a good general hashing function with good distribution.
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The actual function (pseudo code) is:
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for i in i..len(str):
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hash(i) = hash(i - 1) * 65599 + str[i];
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What is included below is the faster version used in gawk. [there is even a faster,
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duff-device version]
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The magic constant 65599 was picked out of thin air while experimenting with
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different constants.
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It turns out to be a prime.
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This is one of the algorithms used in berkeley db (see sleepycat) and elsewhere.
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source: http://www.cse.yorku.ca/~oz/hash.html
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"""
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def sdbm(plain_text: str) -> int:
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"""
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Function implements sdbm hash, easy to use, great for bits scrambling.
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iterates over each character in the given string and applies function to each of
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them.
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>>> sdbm('Algorithms')
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1462174910723540325254304520539387479031000036
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>>> sdbm('scramble bits')
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730247649148944819640658295400555317318720608290373040936089
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"""
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hash_value = 0
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for plain_chr in plain_text:
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hash_value = (
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ord(plain_chr) + (hash_value << 6) + (hash_value << 16) - hash_value
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)
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return hash_value
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