Why is this short code incorrect, "Runtime Error"?

gistfile1.rb

#!/usr/bin/ruby
# http://www.codechef.com/COOK13/problems/DRAGNXOR/
n = gets.to_i
n.times do
  arr = gets.split.map {|i| i.to_i}
  bit = 0
  [1,2].each do |i|
    while arr[i] > 0
      bit += arr[i] % 2
      arr[i] /= 2
    end
  end

  ## Runtime Error
  if bit <= arr[0]
    puts (0..bit-1).inject(0) {|s,i| s+=2**(arr[0]-1-i)}
  else
    puts (0..arr[0]-(bit-arr[0])-1).inject(0) {|s,i| s+=2**(arr[0]-1-i)}
  end

  ## correct code
  #t = [bit, arr[0]-(bit-arr[0])].min -1
  #puts (0..t).inject(0) {|s,i| s+=2**(arr[0]-1-i)}
end