old_contents: print(0 ^ (1 << 80))
  print((1 << 80) ^ (1 << 80))
  print((1 << 80) ^ 0)
  
  a = 0xfffffffffffffffffffffffffffff
  print(a ^ (1 << 100))
  print(a ^ (1 << 200))
  
new_contents: print(0 ^ (1 << 80))
  print((1 << 80) ^ (1 << 80))
  print((1 << 80) ^ 0)
  
  a = 0xfffffffffffffffffffffffffffff
  print(a ^ (1 << 100))
  print(a ^ (1 << 200))
  print(a ^ a == 0)
  
subject: Test that xor result is normalized.