code: public BigDecimal add(BigDecimal augend) {
          if (this.intCompact != INFLATED) {
              if ((augend.intCompact != INFLATED)) {
                  return add(this.intCompact, this.scale, augend.intCompact, augend.scale);
              } else {
                  return add(this.intCompact, this.scale, augend.intVal, augend.scale);
              }
          } else {
              if ((augend.intCompact != INFLATED)) {
                  return add(augend.intCompact, augend.scale, this.intVal, this.scale);
              } else {
                  return add(this.intVal, this.scale, augend.intVal, augend.scale);
              }
          }
      }
docs: Returns a {@code BigDecimal} whose value is {@code (this +
  augend)}, and whose scale is {@code max(this.scale(),
  augend.scale())}.
  
  @param  augend value to be added to this {@code BigDecimal}.
  @return {@code this + augend}