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diff --git a/utils/hyperloglog/hll-err.rb b/utils/hyperloglog/hll-err.rb
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+++ b/utils/hyperloglog/hll-err.rb
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+# hll-err.rb - Copyright (C) 2014 Salvatore Sanfilippo
+# BSD license, See the COPYING file for more information.
+#
+# Check error of HyperLogLog Redis implementation for different set sizes.
+
+require 'rubygems'
+require 'redis'
+require 'digest/sha1'
+
+r = Redis.new
+r.del('hll')
+i = 0
+while true do
+    100.times {
+        elements = []
+        1000.times {
+            ele = Digest::SHA1.hexdigest(i.to_s)
+            elements << ele
+            i += 1
+        }
+        r.pfadd('hll',*elements)
+    }
+    approx = r.pfcount('hll')
+    abs_err = (approx-i).abs
+    rel_err = 100.to_f*abs_err/i
+    puts "#{i} vs #{approx}: #{rel_err}%"
+end