ClickHouse/dbms/scripts/test_intHash32_for_linear_counting.py

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#!/usr/bin/python3
import sys
import math
import statistics as stat
start = int(sys.argv[1])
end = int(sys.argv[2])
#Copied from dbms/src/Common/HashTable/Hash.h
def intHash32(key, salt = 0):
key ^= salt;
key = (~key) + (key << 18);
key = key ^ ((key >> 31) | (key << 33));
key = key * 21;
key = key ^ ((key >> 11) | (key << 53));
key = key + (key << 6);
key = key ^ ((key >> 22) | (key << 42));
return key & 0xffffffff
#Number of buckets for precision p = 12, m = 2^p
m = 4096
n = start
c = 0
m1 = {}
m2 = {}
l1 = []
l2 = []
while n <= end:
c += 1
h = intHash32(n)
#Extract left most 12 bits
x1 = (h >> 20) & 0xfff
m1[x1] = 1
z1 = m - len(m1)
#Linear counting formula
u1 = int(m * math.log(float(m) / float(z1)))
e1 = abs(100*float(u1 - c)/float(c))
l1.append(e1)
print("%d %d %d %f" % (n, c, u1, e1))
#Extract right most 12 bits
x2 = h & 0xfff
m2[x2] = 1
z2 = m - len(m2)
u2 = int(m * math.log(float(m) / float(z2)))
e2 = abs(100*float(u2 - c)/float(c))
l2.append(e2)
print("%d %d %d %f" % (n, c, u2, e2))
n += 1
print("Left 12 bits error: min=%f max=%f avg=%f median=%f median_low=%f median_high=%f" % (min(l1), max(l1), stat.mean(l1), stat.median(l1), stat.median_low(l1), stat.median_high(l1)))
print("Right 12 bits error: min=%f max=%f avg=%f median=%f median_low=%f median_high=%f" % (min(l2), max(l2), stat.mean(l2), stat.median(l2), stat.median_low(l2), stat.median_high(l2)))