ruby-mersenne-twister.rb

=begin
Copyright (c) 2013 Arturs Meinarts

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
=end

module ExtendedFixnum
  module BitOperations
    def last_bits(num)
      result = 0
      num.times{|x| result += self[x] << x}
      result
    end
  end
end

class Fixnum
  include ExtendedFixnum::BitOperations
end

class Bignum
  include ExtendedFixnum::BitOperations
end

class MersenneTwister

  def initialize(seed_num = nil)
    seed_num ||= rand(40227307522636928640) + 1 
    @mt = [] #(0..623).map{0}
    @index = 0
    seed(seed_num)
  end

  def randomize
    generate_numbers
  end

  def random
    extract_number
  end

  private

  def extract_number
    generate_numbers if @index == 0
    
    y = @mt[@index]
    y = y ^ (y >> 11)
    y = y ^ ((y << 7) & 2636928640)
    y = y ^ ((y << 15) & 4022730752)
    y = y ^ (y >> 18)

    @index = (@index + 1) % 624
    y
  end

  def seed(seed_num)    
    @mt[0] = seed_num
    for i in 1..623
      @mt[i] = (1812433253 * (@mt[i-1] ^ (@mt[i-1] >> 30)) + i).last_bits(32)
    end
    true
  end
  
  def generate_numbers
    for i in 0..623
      y = @mt[i][31] + @mt[(i+1) % 624].last_bits(31)
      @mt[i] = @mt[(i + 397) % 624] ^ (y >> 1)
      @mt[i] = @mt[i] ^ 2567483615 if y.odd?
    end
    true
  end
end