code: def _sum2(cp1, cp2, length):
      size = 2
      total = 0
      for i in range(length):
          total += getsample(cp1, size, i) * getsample(cp2, size, i)
      return total
  
imports: import math
  import struct
  from ctypes import create_string_buffer
label_desc: Use image node_id 17 for calling a global function with example usage: _sum2(cp1, cp2, length) and returns: total