布隆過濾器

from .defaults import BLOOMFILTER_BIT, BLOOMFILTER_HASH_NUMBER


class HashMap(object):
def __init__(self, m, seed):
self.m = m
self.seed = seed

def hash(self, value):
"""
Hash Algorithm
:param value: Value
:return: Hash Value
"""
ret = 0
for i in range(len(value)):
ret += self.seed * ret + ord(value[i])
return (self.m - 1) & ret


class BloomFilter(object):
def __init__(self, server, key, bit=BLOOMFILTER_BIT, hash_number=BLOOMFILTER_HASH_NUMBER):
"""
Initialize BloomFilter
:param server: Redis Server
:param key: BloomFilter Key
:param bit: m = 2 ^ bit
:param hash_number: the number of hash function
"""
# default to 1 << 30 = 10,7374,1824 = 2^30 = 128MB, max filter 2^30/hash_number = 1,7895,6970 fingerprints
self.m = 1 << bit
self.seeds = range(hash_number)
self.server = server
self.key = key
self.maps = [HashMap(self.m, seed) for seed in self.seeds]

def exists(self, value):
"""
if value exists
:param value:
:return:
"""
if not value:
return False
exist = True
for map in self.maps:
offset = map.hash(value)
exist = exist & self.server.getbit(self.key, offset)
return exist

def insert(self, value):
"""
add value to bloom
:param value:
:return:
"""
for f in self.maps:
offset = f.hash(value)
self.server.setbit(self.key, offset, 1)