string_hash_18.rb

class String
  def hash18
    # cheeky integer truncate TODO move to bitmask, and method
    trunc = lambda { |v| [v].pack('i').unpack('i').first }
    key = 0
    each_byte do |b|
      key = trunc.call(trunc.call(key*65599) + b)
    end
    trunc.call(key + trunc.call(key >> 5))
  end
end

require 'rubygems'
require 'minitest/unit'
include MiniTest::Assertions

chars = %w[
  a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9
]
chash = [
  100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114,
  115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 49, 50, 51, 52, 53,
  54, 55, 56, 57, 58
]

chars.zip(chash).each do |s, e|
  assert_equal e, s.hash18, "#{s.inspect}.hash18()"
end

strings = %w[abc def ghi jkl]
hashes = [833038373, 858800354, 884562335, 910324316]

strings.zip(hashes).each do |s, e|
  assert_equal e, s.hash18, "#{s.inspect}.hash18()"
end

lorems = %w[
  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus dolor
  urna, pulvinar eget laoreet pretium, vehicula nec mi. Nunc aliquam sapien
  rhoncus nisl euismod eu accumsan justo consectetur. Nam vel ante eget libero
  interdum porttitor. Ut dolor arcu, dignissim sit amet aliquam at, ultricies
  at ante. Morbi vehicula dignissim orci, in semper est pretium ut. Proin at
  odio nulla. Vivamus posuere, lectus ac ultrices suscipit, neque orci euismod
  arcu, nec ullamcorper eros elit ornare dolor. Phasellus metus tellus,
  consectetur et tincidunt eu, congue vel eros. Nam ac tortor nunc, vel auctor
  erat. Mauris consectetur est sed nisl blandit placerat. Duis arcu ligula,
  dictum vel euismod a, sagittis gravida purus. Nulla sit amet ullamcorper
  lectus. Vivamus condimentum pellentesque tristique.
]

lorems_hashes = lorems.map { |s| s.hash }

lorems.zip(lorems_hashes).each do |s, e|
  assert_equal e, s.hash18, "#{s.inspect}.hash18()"
end

bigstr = <<-PLAIN
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus dolor urna,
pulvinar eget laoreet pretium, vehicula nec mi. Nunc aliquam sapien rhoncus
nisl euismod eu accumsan justo consectetur. Nam vel ante eget libero interdum
porttitor. Ut dolor arcu, dignissim sit amet aliquam at, ultricies at ante.
Morbi vehicula dignissim orci, in semper est pretium ut. Proin at odio nulla.
Vivamus posuere, lectus ac ultrices suscipit, neque orci euismod arcu, nec
ullamcorper eros elit ornare dolor. Phasellus metus tellus, consectetur et
tincidunt eu, congue vel eros. Nam ac tortor nunc, vel auctor erat. Mauris
consectetur est sed nisl blandit placerat. Duis arcu ligula, dictum vel
euismod a, sagittis gravida purus. Nulla sit amet ullamcorper lectus. Vivamus
condimentum pellentesque tristique.
PLAIN

bigstr_hash = bigstr.hash

assert_equal bigstr_hash, bigstr.hash18, "#{bigstr.inspect}.hash18()"