Need help using an implementation of XTEA in Java

I need to encrypt some String using XTEA algorithm, and found this code but I'm not sure how to use it and I get a java.lang.ArrayIndexOutOfBoundsException.

Here's how I'm using it:

XTEA mXTEA = new XTEA();        
mXTEA.setKey(XTEA_KEY.getBytes());
byte[] b = someString.getBytes();
mXTEA.encrypt(b, 0, b.length);

More specifically, I'm not sure what are the last two parameters of encrypt. I assumed that off is some offset and len is the length of the input stream.

Edit

Her's the full stack trace:

08-12 16:42:03.475: E/AndroidRuntime(23894): Caused by: java.lang.ArrayIndexOutOfBoundsException: length=14; index=14
08-12 16:42:03.475: E/AndroidRuntime(23894):    at   xxx.XTEA.encryptBlock(XTEA.java:56)
08-12 16:42:03.475: E/AndroidRuntime(23894):    at xxx.XTEA.encrypt(XTEA.java:43)

Anybody can help?

Answer

As suggested by John Skeet, I the string must be padded to get to a multiple of 8:

int len = myString.length();
int newLen = len + (8- len % 8);

while(myString.length()<newSize){
    myString += "\0";
}

Solution

Looking at the code and the Wikipedia entry on XTEA it looks like the problem is that it only works on blocks of 8 bytes, and you're providing 14 bytes (which isn't a multiple of 8).

You'll probably need to add some padding, and either just chop off trailing 0s from the plaintext, or if you need to be able to represent U+0000 in the actual text, you could add a bit of data to say how much real data there is.