Method optArith

basex-core/src/main/java/org/basex/query/expr/CmpG.java:141–172

Tries to rewrite arithmetic operations. @param cc compilation context @return optimized or original expression @throws QueryException query exception

(final CompileContext cc)

   * @throws QueryException query exception
   */
  private Expr optArith(final CompileContext cc) throws QueryException {
    final Expr expr1 = exprs[0], expr2 = exprs[1];
    Expr ex = null;

    if(expr1 instanceof final Arith arth && expr2.seqType().instanceOf(Types.NUMERIC_O)) {
      final Expr op11 = expr1.arg(0), op12 = expr1.arg(1), op22 = expr2.arg(1);
      final double num12 = op12 instanceof final ANum num ? num.dbl() : Double.NaN;
      if(op12.seqType().instanceOf(Types.NUMERIC_O)) {
        final Calc calc1 = arth.calc;
        if(calc1 == Calc.SUBTRACT && expr2 == Itr.ZERO) {
          // E - NUMERIC = 0 → E = NUMERIC
          ex = new CmpG(info, op11, op12, op);
        } else if((
          POSITION.is(op11) ||
          !Double.isNaN(num12) &&
          (expr2 instanceof ANum || expr2 instanceof Arith && op22 instanceof ANum)
        ) && (
          calc1.oneOf(Calc.ADD, Calc.SUBTRACT) ||
          calc1.oneOf(Calc.MULTIPLY, Calc.DIVIDE) && num12 != 0 &&
            (op.oneOf(CmpOp.EQ, CmpOp.NE) || num12 > 0)
        )) {
          // position() + 1 < last() → position() < last() - 1
          // count(E) div 2 = 1 → count(E) = 1 * 2
          // $a - 1 = $b + 1 → $a = $b + 2
          // $x * -1 = 1 → $x = 1 div -1  (no rewrite if RHS of */div (<,<=,>=,>) is negative)
          final Expr arg2 = new Arith(info, expr2, op12, calc1.invert()).optimize(cc);
          ex = new CmpG(info, op11, arg2, op);
        }
      }
    }
    return ex != null ? ex.optimize(cc) : this;
  }

  @Override
  public final Bln item(final QueryContext qc, final InputInfo ii) throws QueryException {