code: public int decrease(double extrp, int decrease)
      {
          final int remain = getCurrent();
          final double decreased = remain - decrease * extrp;
          set(decreased);
          if (decreased < 0)
          {
              return remain;
          }
          return decrease;
      }
docs: Decrease current value. The current value will not be lower than 0.
  
  @param extrp The extrapolation value.
  @param decrease The decrease step.
  @return The decreased value (equal to decrease in normal case, lower in other case).