# Random number generation based on code from GST-3.2.5 (2.02)
# @see qmjAJh
 
class PiRandom
  def initialize
    self.seed(Time.now.to_f)
  end
 
  def seed(value)
    @state = (value / 100000.0 + value) % 1.0
    self.rand
    self.rand
  end
 
  def rand(*args)
    case args.size
    when 0
      @state = ((@state + Math::PI) ** 4) % 1.0
    when 1
      rand_with(args.first)
    else
      raise ArgumentError.new("wrong number of arguments "\
            "(given #{args.size}, expected 0..1)")
    end
  end
 
  private def rand_with(arg)
    case arg
    when Float
      # [0, arg) exclusive.
      self.rand * [arg, 0].max
    when Integer
      # [0, arg] inclusive.
      rand_with(arg + 1.0).to_i
    when Range
      min = arg.min
      max = arg.max
      raise ArgumentError.new("invalid argument: #{arg}")\
            if min.nil? || max.nil?
      rand_with(max - min) + min
    else
      raise TypeError.new("no support for: #{arg.class}")
    end
  end
end
 
# Test.
 
require "test/unit"
extend Test::Unit::Assertions
 
def chi_square(n, r, prng)
  f = Array.new(r, 0)
  n.times do
    f[prng.rand(0...r)] += 1
  end
  t = f.sum {|x| x * x}
  r * t / n - n
end
 
prng = PiRandom.new
 
# Distribution.
 
5.times do
  p chi_square(1000, 100, prng)
end
 
n = 100
 
# Canonical.
 
n.times do
  assert do
    t = prng.rand
    0.0 <= t && t < 1.0
  end
end
 
# Max.
 
n.times do
  assert do
    t = prng.rand(5)
    0 <= t && t <= 5
  end
  assert do
    t = prng.rand(5.0)
    0.0 <= t && t < 5.0
  end
end
 
# Range.
 
n.times do
  assert do
    t = prng.rand(1..5)
    1 <= t && t <= 5
  end
  assert do
    t = prng.rand(1...5)
    1 <= t && t < 5
  end
  assert do
    t = prng.rand(1.0..5.0)
    1.0 <= t && t < 5.0
  end
end

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