http://weblog.riywo.com/post/31254453611の追試。str.bytes.inject(&:+) % num でも均等に散ってた. 結局のところ入力文字の分布によるわけだが、入力文字の分布はわからんのでおいとく

hash_test.rb

require 'digest/md5'
require 'digest/sha1'
require 'digest/sha2'
require 'murmurhash3'
num = 5 
test = 10000

def str(len)
  (("a".."z").to_a + ("A".."Z").to_a + (0..9).to_a).shuffle[0,len].join
end

res = { 
  "raw"         => Array.new(num, 0), 
  "md5"         => Array.new(num, 0), 
  "sha1"        => Array.new(num, 0), 
  "sha256"      => Array.new(num, 0), 
  "murmurhash3" => Array.new(num, 0), 
}

base = str(10) + "." + str(10) + "." + str(10)
test.times {
  str = base + "." + str(10) # construct string like typical fluentd tags (like the last one is hostname)
  res["raw"][str.bytes.inject(&:+) % num] += 1
  res["md5"][Digest::MD5::hexdigest(str).bytes.inject(&:+) % num] += 1
  res["sha1"][Digest::SHA1::hexdigest(str).bytes.inject(&:+) % num] += 1
  res["sha256"][Digest::SHA256::hexdigest(str).bytes.inject(&:+) % num] += 1
  res["murmurhash3"][MurmurHash3::V32.str_hash(str) % num] += 1
}
 
res.each_pair {|k, v|
  rate = v.map {|x|
    (x.to_f / test * 100).to_i
  }
  p sprintf "%15s => %p", k, rate
}

"            raw => [19, 20, 19, 19, 20]"
"            md5 => [20, 19, 19, 19, 20]"
"           sha1 => [19, 20, 19, 19, 19]"
"         sha256 => [20, 19, 19, 20, 20]"
"    murmurhash3 => [20, 19, 20, 19, 20]"