code: public long addWrapField(long instant, int amount) {
          return set(instant, FieldUtils.getWrappedValue(get(instant), amount, iMin, iMax));
      }
docs: Add to the scaled component of the specified time instant,
  wrapping around within that component if necessary.
  
  @param instant  the time instant in millis to update.
  @param amount  the amount of scaled units to add (can be negative).
  @return the updated time instant.