code: def findmax(cp, len2):
      size = 2
      sample_count = _sample_count(cp, size)
  
      if len(cp) % 2 != 0:
          raise error("Strings should be even-sized")
  
      if len2 < 0 or sample_count < len2:
          raise error("Input sample should be longer")
  
      if sample_count == 0:
          return 0
  
      result = _sum2(cp, cp, len2)
      best_result = result
      best_i = 0
  
      for i in range(1, sample_count - len2 + 1):
          sample_leaving_window = getsample(cp, size, i - 1)
          sample_entering_window = getsample(cp, size, i + len2 - 1)
  
          result -= sample_leaving_window**2
          result += sample_entering_window**2
  
          if result > best_result:
              best_result = result
              best_i = i
  
      return best_i
  
imports: import math
  import struct
  from ctypes import create_string_buffer
label_desc: Use image node_id 20 for calling a global function with example usage: findmax(cp, len2) and returns: best_i, int