Mitja HORVAT
bcae51ead9
This better matches what one would expect from the hex or base64 (upcoming) formats.
41 lines
1.1 KiB
Python
41 lines
1.1 KiB
Python
import math
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class BhashException(Exception): pass
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class Bhash:
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"""
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Hash manipulation class.
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The hash is internally treated as a big-endinan integer. This allows for
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easy implementation of operations such as modulo.
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Note: The consumed bits are calculated using math.log() so the exact number
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may be inprecise.
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"""
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def __init__(self):
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self.bhash = None
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self.bits_avail = 0
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self.bits_used = 0.0
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def from_bytes(self, buf: bytes):
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"""
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Initialize a Bhash from a bytes object
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"""
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self.bhash = int.from_bytes(buf, byteorder='little')
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self.bits_avail = len(buf) * 8
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self.bits_used = 0.0
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def modulo(self, mod: int) -> int:
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"""
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Treat the hash as a bigint and divide it by mod. The hash is updated
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with the division result while the module value is returned.
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"""
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self.bits_used += math.log(mod) / math.log(2)
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if self.bits_used > self.bits_avail:
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raise BhashException("Consumed all bits in hash")
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r = self.bhash % mod
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self.bhash //= mod
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return r
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