code: void set3(int newPrice, int optCur, int back2, int len2, int back) {
          price = newPrice;
          optPrev = optCur + len2 + 1;
          backPrev = back;
          prev1IsLiteral = true;
          hasPrev2 = true;
          optPrev2 = optCur;
          backPrev2 = back2;
      }
docs: Sets to indicate three LZMA symbols of which the second one
  is a literal.