code: private int getArgIndex(final int arg) {
          int index = (access & Opcodes.ACC_STATIC) == 0 ? 1 : 0;
          for (int i = 0; i < arg; i++) {
              index += argumentTypes[i].getSize();
          }
          return index;
      }
docs: Returns the index of the given method argument in the frame's local
  variables array.
  
  @param arg
  the index of a method argument.
  @return the index of the given method argument in the frame's local
  variables array.