- /* Start from this hash. */
- *hash = chain->known[i].hash;
-
- /* This indicates the bits which are in 'index' and
- * not the key */
- diff = index ^ chain->known[i].index;
-
- /* Using ilog64 here is an optimization. */
- derive(~diff, ilog64(diff), hash);
+ derive(chain->known[i].index, index, &chain->known[i].hash,
+ hash);