bloom

bloom.py

@@ -0,0 +1,55 @@
+import random
+
+try: #
+    shathree = __import__('sha3').sha3_256
+except:
+    shathree = __import__('python_sha3').sha3_256
+
+
+params = {
+    "size": 256,
+    "pecks": 32
+}
+
+
+def decode_int(x):
+    o = 0
+    for a in x:
+        o = o * 256 + ord(a)
+    return o
+
+
+def sha3(x):
+    return shathree(x).digest()
+
+
+def bloom_insert(params, bloom, val):
+    k = decode_int(sha3(val)) * (3**160 + 112)
+    for i in range(params["pecks"]):
+        bloom |= 1 << (k % params["size"])
+        k //= params["size"]
+    return bloom
+
+
+def bloom_query(params, bloom, val):
+    o = bloom_insert(params, 0, val)
+    return (bloom & o) == o
+
+
+def test_params(size, pecks, objcount):
+    params = {"size": size, "pecks": pecks}
+    count = 0
+    for i in range(100):
+        objs = [str(random.randrange(2**40)) for i in range(objcount)]
+        bloom = 0
+        for o in objs:
+            bloom = bloom_insert(params, bloom, o)
+    
+        for o in objs:
+            assert bloom_query(params, bloom, o)
+    
+        for i in range(100):
+            if bloom_query(params, bloom, str(random.randrange(2**40))):
+                count += 1
+    
+    print 'False positive rate: %f' % (count / 10000.)