code: def add(cp1, cp2, size):
      _check_params(len(cp1), size)
  
      if len(cp1) != len(cp2):
          raise error("Lengths should be the same")
  
      clip = _get_clipfn(size)
      sample_count = _sample_count(cp1, size)
      result = create_string_buffer(len(cp1))
  
      for i in range(sample_count):
          sample1 = getsample(cp1, size, i)
          sample2 = getsample(cp2, size, i)
  
          sample = clip(sample1 + sample2)
  
          _put_sample(result, size, i, sample)
  
      return result.raw
  
imports: import math
  import struct
  from ctypes import create_string_buffer
label_desc: Use image node_id 27 for calling a global function with example usage: add(cp1, cp2, size) and returns: result