pidigits.rb

# The Computer Language Benchmarks Game
# http://shootout.alioth.debian.org/

# transliterated from Mario Pernici's Python program
# contributed by Rick Branson
# made 'functional' by Sam Rawlins

require "rubygems"
require "gmp"

def gmpz(n)
  GMP::Z.new(n)
end

N = gmpz((ARGV[0] || 100).to_i)

i = gmpz(0); k = gmpz(0); ns = gmpz(0)
k1 = gmpz(1)
n,a,d,t,u = [1,0,1,0,0].map { |n| gmpz(n) }

g_zero = gmpz(0)
g_one = gmpz(1)
g_two = gmpz(2)
g_three = gmpz(3)
g_ten = gmpz(10)

loop do
  GMP::Z.add(k,  k,  g_one)
  t = n << g_one
  GMP::Z.mul(n,  n,  k)
  GMP::Z.add(a,  a,  t)
  GMP::Z.add(k1, k1, g_two)
  GMP::Z.mul(a,  a,  k1)
  GMP::Z.mul(d,  d,  k1)
  if a >= n
    q = (n*g_three +a)
    t = q.fdiv(d)
    u = q.fmod(d)
    GMP::Z.add(u, u, n)
    if d > u
      ns = ns * g_ten + t
      GMP::Z.add(i, i, g_one)
      if i % g_ten == g_zero
        puts "#{ns.to_s.rjust(10, '0')}\t:#{i.to_s}"
        ns = g_zero
      end
      break if i >= N
   
      GMP::Z.submul(a, d, t)
      GMP::Z.mul(   a, a, g_ten)
      GMP::Z.mul(   n, n, g_ten)
    end
  end
end