modpow.py

n = random.randrange(m)
def modpow(a, n, m):
  r = 1
  while n > 0:
    if n & 1 == 1:
      r = (r * a) % m
      n = n >> 1
      a = (a * a) % m

modpow.rb

n = rand(m)
def modpow(a, n, m) 
  r = 1
  loop do
    r = r * a % m if n[0] == 1
    n >>= 1
    return r if n == 0
    a = a * a % m
  end
end