public override ValueEval Evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1)
        {
            ValueEval vA;
            ValueEval vB;

            try
            {
                vA = OperandResolver.GetSingleValue(arg0, srcRowIndex, srcColumnIndex);
                vB = OperandResolver.GetSingleValue(arg1, srcRowIndex, srcColumnIndex);
            }
            catch (EvaluationException e)
            {
                return(e.GetErrorEval());
            }
            int  cmpResult = DoCompare(vA, vB);
            bool result    = ConvertComparisonResult(cmpResult);

            return(BoolEval.ValueOf(result));
        }
 private static int CompareBlank(ValueEval v)
 {
     if (v == BlankEval.instance)
     {
         return(0);
     }
     if (v is BoolEval)
     {
         BoolEval boolEval = (BoolEval)v;
         return(boolEval.BooleanValue ? -1 : 0);
     }
     if (v is NumberEval)
     {
         NumberEval ne = (NumberEval)v;
         //return ne.NumberValue.CompareTo(0.0);
         return(NumberComparer.Compare(0.0, ne.NumberValue));
     }
     if (v is StringEval)
     {
         StringEval se = (StringEval)v;
         return(se.StringValue.Length < 1 ? 0 : -1);
     }
     throw new ArgumentException("bad value class (" + v.GetType().Name + ")");
 }
        private static int DoCompare(ValueEval va, ValueEval vb)
        {
            // special cases when one operand is blank
            if (va == BlankEval.instance)
            {
                return(CompareBlank(vb));
            }
            if (vb == BlankEval.instance)
            {
                return(-CompareBlank(va));
            }

            if (va is BoolEval)
            {
                if (vb is BoolEval)
                {
                    BoolEval bA = (BoolEval)va;
                    BoolEval bB = (BoolEval)vb;
                    if (bA.BooleanValue == bB.BooleanValue)
                    {
                        return(0);
                    }
                    return(bA.BooleanValue ? 1 : -1);
                }
                return(1);
            }
            if (vb is BoolEval)
            {
                return(-1);
            }
            if (va is StringEval)
            {
                if (vb is StringEval)
                {
                    StringEval sA = (StringEval)va;
                    StringEval sB = (StringEval)vb;
                    return(string.Compare(sA.StringValue, sB.StringValue, StringComparison.OrdinalIgnoreCase));
                }
                return(1);
            }
            if (vb is StringEval)
            {
                return(-1);
            }
            if (va is NumberEval)
            {
                if (vb is NumberEval)
                {
                    NumberEval nA = (NumberEval)va;
                    NumberEval nB = (NumberEval)vb;
                    if (nA.NumberValue == nB.NumberValue)
                    {
                        // Excel considers -0.0 == 0.0 which is different to Double.compare()
                        return(0);
                    }
                    return(NumberComparer.Compare(nA.NumberValue, nB.NumberValue));
                }
            }
            throw new ArgumentException("Bad operand types (" + va.GetType().Name + "), ("
                                        + vb.GetType().Name + ")");
        }