Parsing expressions back and forth

Question

I'm using JEP ( http://www.singularsys.com/jep/ ) to parse expressions and calculate values from bytes. I'm trying to avoid having to have my users create an expression to calculate the real value and back to the byte.
Right now, I'm looping through (while i < 255) and for a single byte, that seems to be fine. However, there are times I have to test two bytes (65536) and perhaps more, and its way too slow. I was just wondering if there is another option.
Below is an example of the relevent code -- it's really ugly and it's not quite working properly for multiple bytes, but I'd like to find a better solution rather than messing with this. Thanks for the help!
        double previousValue = 0;
        int input = Integer.parseInt(inputString);
        boolean isInverse = false;
        // check whether expression is division
        if (table.getScale().getIncrement() < 0) {
            isInverse = true;
            previousValue = calcDisplayValue(2);
        for (int i = 0; i < Math.pow(256, table.getStorageType()); i += Math.pow(256, table.getStorageType() - 1)) {
            if (!(isInverse && i == 0)) {
                double nextValue = calcDisplayValue(i);
                if (input <= Math.max(previousValue, nextValue) && input >= Math.min(previousValue, nextValue)) {
                    if (i < Math.pow(256, table.getStorageType() - 1)) {                       
                        if (input - nextValue < input - previousValue) setBinValue(i - 1);
                        else setBinValue(i);
                        break;                   
                    } else {
                        for (int z = 0; z < 256; z++) {                          
                            nextValue = calcDisplayValue(i + z);             
                            if (input <= Math.max(previousValue, nextValue) && input >= Math.min(previousValue, nextValue)) {                     
                                if (input - nextValue < input - previousValue) setBinValue(i * 256 + z - 1);
                                else setBinValue(i * 256 + z);
                                break;          
                            } else previousValue = nextValue;
                } else previousValue = nextValue;
    }

Answer 1

I found a library called XJEP which will apparantly parse complete equations instead of just expressions, but this will double the size of my application. Are there any other options?