Using 32 bit integers

Question

I need to use a 32bit integer in my app, but Java Card only supports 16 bit integers. What's the best way of handling this? I've been trying to do it with a 4 byte array but I'm having problems add/subtracting. I've made the following function to adding two byte array integers together
     public static byte [] intAdd(byte [] firstInt, byte[] secondInt) {
          if (firstInt.length != 4 || secondInt.length != 4) ISOException.throwIt(ISO7816.SW_WRONG_DATA);
          byte [] result = new byte[4];
          byte carry = (byte)0x00;
          for (int i=3; i>=0; i--) {
               int tmp = firstInt[i] + secondInt[i] + carry;
               byte[] tmpb = intToBytes(tmp);
               result[i] = tmpb[3];
               carry = tmpb[2];
          return result;
It doesn't work properly because java treats each individual byte as a signed integer. Plus I think this is horribly inefficient.

Answer 1

797530 wrote:
     public static byte [] intAdd(byte [] firstInt, byte[] secondInt)  {
          if (firstInt.length != 4 || secondInt.length != 4) ISOException.throwIt(ISO7816.SW_WRONG_DATA);
          byte [] result = new byte[4];
          byte carry = (byte)0x00;
          for (int i=3; i>=0; i--) {
               int tmp = ((short)firstInt[i] & 0x00FF) + ((short)secondInt[i] & 0x00FF) + carry;
               byte[] tmpb = intToBytes(tmp);
               result[i] = tmpb[3];
               carry = tmpb[2];
          return result;
Please you code tags when posting code.
In the code you have posted there is a memory leak and your card will run out of EEPROM eventually. You should only ever use the new keyword in your applet constructor or code that is only ever called from the applet constructor as there is (essentially) no garbage collector.