int fib_table_lookup(struct fib_table *tb, const struct flowi4 *flp,
		     struct fib_result *res, int fib_flags)
{
	struct trie *t = (struct trie *) tb->tb_data;
…
	const t_key key = ntohl(flp->daddr);
…
	/* Step 1: Travel to the longest prefix match in the trie */
	for (;;) {
		index = get_cindex(key, n);
…
	}

	/* Step 2: Sort out leaves and begin backtracing for longest prefix */
	for (;;) {
…
			/* strip the least significant bit from the cindex */
			cindex &= cindex - 1;
…
	}

found:
	/* this line carries forward the xor from earlier in the function */
	index = key ^ n->key;

	/* Step 3: Process the leaf, if that fails fall back to backtracing */
	hlist_for_each_entry_rcu(fa, &n->leaf, fa_list) {
		struct fib_info *fi = fa->fa_info;
…
		if ((BITS_PER_LONG > KEYLENGTH) || (fa->fa_slen < KEYLENGTH)) {
			if (index >= (1ul << fa->fa_slen))
				continue;
		}
…
		err = fib_props[fa->fa_type].error;
		if (unlikely(err < 0)) {
…
			return err;
		}
…
			res->prefix = htonl(n->key);
			res->prefixlen = KEYLENGTH - fa->fa_slen;

Warm-up