I cribbed the public domain TEA source from wikipedia ( http://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm ), looks like this -

<code>
void encrypt (uint32_t* v, uint32_t* k) {
    uint32_t v0=v[0], v1=v[1], sum=0, i;           /* set up */
    uint32_t delta=0x9e3779b9;                     /* a key schedule constant */
    uint32_t k0=k[0], k1=k[1], k2=k[2], k3=k[3];   /* cache key */
    for (i=0; i < 32; i++) {                       /* basic cycle start */
        sum += delta;
        v0 += ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
        v1 += ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);
    }                                              /* end cycle */
    v[0]=v0; v[1]=v1;
}
</code>

It works fine, but I am trying to understand crypto a little more so I am tweaking and exploring. I would have thought that changing the number of rounds (32 in the example) would work great as long as the decrypt function changed to use the same number. However, I bumped it to 50 on each side and now my output does not match the initial plaintext. Thinking that may be too high, I tried 20. Also broken. Then I tried 31 and 33! Both broken.

Is the number of rounds in TEA required to be 32 for some reason? I cannot see why, but I am far from expert.