code: func getMiddle(lowStr, highStr string) *big.Int {
  	low := bigIntFromStr(lowStr, 10)
  	high := bigIntFromStr(highStr, 10)
  	if low.Cmp(high) != -1 {
  		die(false, "Error: %s is not smaller than %s", lowStr, highStr)
  	}
  	middle := new(big.Int)
  	middle = middle.Div(middle.Add(low, high), big.NewInt(2))
  	return middle
  }
docs: //
  // Big int (for 128-bit start/end hash keys) helper functions
  //
  // Takes two large base 10 numeric strings a and b, and returns (a + b)/2