code: def diff_bisectSplit(self, text1, text2, x, y, deadline):
      
      text1a = text1[:x]
      text2a = text2[:y]
      text1b = text1[x:]
      text2b = text2[y:]
  
      # Compute both diffs serially.
      diffs = self.diff_main(text1a, text2a, False, deadline)
      diffsb = self.diff_main(text1b, text2b, False, deadline)
  
      return diffs + diffsb
docs: Given the location of the 'middle snake', split the diff in two parts
      and recurse.
  
      Args:
        text1: Old string to be diffed.
        text2: New string to be diffed.
        x: Index of split point in text1.
        y: Index of split point in text2.
        deadline: Time at which to bail if not yet complete.
  
      Returns:
        Array of diff tuples.