class RSpec::Core::Backports::Random::MT19937

def random_integer(upto)
  n = upto - 1
  nb_full_32 = 0
  while n > PAD_32_BITS
    n >>= 32
    nb_full_32 += 1
  end
  mask = mask_32_bits(n)
  begin
    rand = random_32_bits & mask
    nb_full_32.times do
      rand <<= 32
      rand |= random_32_bits
    end
  end until rand < upto
  rand
end