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Commit 6ab94a3f authored by Hans Boehm's avatar Hans Boehm
Browse files

Generalize % operator: Handle 100+10% as expected 

Bug: 22836179

Handle + or - operators specially if they are followed by a constant
or pre-evaluated expression and the % operator.

Since this is basically an idiomatic use of the operators, we
apply it very conservatively.  When in doubt we use the old
interpretation.

Also fixes one unrelated anachronism in a comment.

Change-Id: I2f9fd26dd6c0456f0210815ef2bc1afca3a2b4d7
(cherry picked from commit 8afd0f85)
parent b7bd3488

src/com/android/calculator2/CalculatorExpr.java

+71 −9
Original line number Diff line number Diff line
@@ -310,7 +310,7 @@ class CalculatorExpr { 
        }

        // In writing out PreEvals, we are careful to avoid writing

        // out duplicates.  We assume that two expressions are

        // duplicates if they have the same mVal.  This avoids a

        // duplicates if they have the same CR value.  This avoids a

        // potential exponential blow up in certain off cases and

        // redundant evaluation after reading them back in.

        // The parameter hash map maps expressions we've seen
@@ -1022,6 +1022,58 @@ class CalculatorExpr { 
        return new EvalRet(cpos, crVal, ratVal);

    }



    /**

     * Is the subexpression starting at pos a simple percent constant?

     * This is used to recognize exppressions like 200+10%, which we handle specially.

     * This is defined as a Constant or PreEval token, followed by a percent sign, and followed

     * by either nothing or an additive operator.

     * Note that we are intentionally far more restrictive in recognizing such expressions than

     * e.g. http://blogs.msdn.com/b/oldnewthing/archive/2008/01/10/7047497.aspx .

     * When in doubt, we fall back to the the naive interpretation of % as 1/100.

     * Note that 100+(10)% yields 100.1 while 100+10% yields 110.  This may be controversial,

     * but is consistent with Google web search.

     */

    private boolean isPercent(int pos) {

        if (mExpr.size() < pos + 2 || !isOperatorUnchecked(pos + 1, R.id.op_pct)) {

            return false;

        }

        Token number = mExpr.get(pos);

        if (number instanceof Operator) {

            return false;

        }

        if (mExpr.size() == pos + 2) {

            return true;

        }

        if (!(mExpr.get(pos + 2) instanceof Operator)) {

            return false;

        }

        Operator op = (Operator) mExpr.get(pos + 2);

        return op.id == R.id.op_add || op.id == R.id.op_sub;

    }



    /**

     * Compute the multiplicative factor corresponding to an N% addition or subtraction.

     * @param pos position of Constant or PreEval expression token corresponding to N

     * @param isSubtraction this is a subtraction, as opposed to addition

     * @param ec usable evaluation contex; only length matters

     * @return Rational and CR values; position is pos + 2, i.e. after percent sign

     */

    private EvalRet getPercentFactor(int pos, boolean isSubtraction, EvalContext ec)

            throws SyntaxException {

        EvalRet tmp = evalUnary(pos, ec);

        BoundedRational ratVal = isSubtraction ? BoundedRational.negate(tmp.ratVal)

                : tmp.ratVal;

        CR crVal = isSubtraction ? tmp.val.negate() : tmp.val;

        ratVal = BoundedRational.add(BoundedRational.ONE,

                BoundedRational.multiply(ratVal, RATIONAL_ONE_HUNDREDTH));

        if (ratVal == null) {

            crVal = CR.ONE.add(crVal.multiply(REAL_ONE_HUNDREDTH));

        } else {

            crVal = ratVal.CRValue();

        }

        return new EvalRet(pos + 2 /* after percent sign */, crVal, ratVal);

    }



    private EvalRet evalExpr(int i, EvalContext ec) throws SyntaxException {

        EvalRet tmp = evalTerm(i, ec);

        boolean is_plus;
@@ -1030,6 +1082,15 @@ class CalculatorExpr { 
        BoundedRational ratVal = tmp.ratVal;

        while ((is_plus = isOperator(cpos, R.id.op_add, ec))

               || isOperator(cpos, R.id.op_sub, ec)) {

            if (isPercent(cpos + 1)) {

                tmp = getPercentFactor(cpos + 1, !is_plus, ec);

                ratVal = BoundedRational.multiply(ratVal, tmp.ratVal);

                if (ratVal == null) {

                    crVal = crVal.multiply(tmp.val);

                } else {

                    crVal = ratVal.CRValue();

                }

            } else {

                tmp = evalTerm(cpos + 1, ec);

                if (is_plus) {

                    ratVal = BoundedRational.add(ratVal, tmp.ratVal);
@@ -1046,6 +1107,7 @@ class CalculatorExpr { 
                        crVal = ratVal.CRValue();

                    }

                }

            }

            cpos = tmp.pos;

        }

        return new EvalRet(cpos, crVal, ratVal);