rand, srand - pseudo-random number generator of POSIX.1 example implementation for Ruby.

POSIX1_rand.rb

# Copyright (c) 2013 Koichi OKADA. All rights reserved.
# This script is distributed under the MIT license.
# http://www.opensource.org/licenses/mit-license.php

# rand, srand - pseudo-random number generator of POSIX.1 example implementation for Ruby.
# see
# Wikipedia / POSIX
#     http://ja.wikipedia.org/wiki/POSIX
# The Linux man-pages project / rand(3)
#     https://www.kernel.org/doc/man-pages/
#     http://man7.org/linux/man-pages/man3/rand.3.html
# JM / rand(3)
#     http://linuxjm.sourceforge.jp/
#     http://linuxjm.sourceforge.jp/html/LDP_man-pages/man3/rand.3.html
# POSIX.1-2008 / XSH / rand
#     http://pubs.opengroup.org/onlinepubs/9699919799/
#     http://pubs.opengroup.org/onlinepubs/9699919799/functions/rand.html
module POSIX1
  class Rand
    def self.rand
      DEFAULT.rand
    end
    def self.frand
      rand() / (RAND_MAX + 1.0)
    end
    def self.srand seed
      DEFAULT.srand seed
    end
    
    def initialize seed = nil
      srand seed
    end
    def rand
      @next =  @next * 1103515245 + 12345
      @next = (@next / 65536).floor % (RAND_MAX + 1)
    end
    def frand
      rand / (RAND_MAX + 1.0)
    end
    def srand seed = nil
      @next = seed.nil? ? Random.new.rand(RAND_MAX) : seed.to_i
    end
    
    RAND_MAX  = 32767
    DEFAULT = self.new
  end
  
  module_function
  
  def rand
    Rand.rand
  end
  def frand
    Rand.frand
  end
  def srand seed = nil
    Rand.srand seed
  end
end