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31 #ifndef __BASE_TRIE_HH__
32 #define __BASE_TRIE_HH__
34 #include "base/cprintf.hh"
35 #include "base/misc.hh"
36 #include "base/types.hh"
38 // Key has to be an integral type.
39 template <class Key, class Value>
51 return (test & mask) == key;
59 Node(Key _key, Key _mask, Value *_val) :
60 key(_key & _mask), mask(_mask), value(_val),
85 for (int i = 1; i < level; i++) {
92 cprintf("(%p, %p, %#X, %#X, %p)\n", parent, this, key, mask, value);
94 kids[0]->dump(level + 1);
96 kids[1]->dump(level + 1);
104 typedef Node *Handle;
106 Trie() : head(0, 0, NULL)
109 static const unsigned MaxBits = sizeof(Key) * 8;
113 * A utility method which checks whether the key being looked up lies
114 * beyond the Node being examined. If so, it returns true and advances the
115 * node being examined.
116 * @param parent The node we're currently "at", which can be updated.
117 * @param kid The node we may want to move to.
118 * @param key The key we're looking for.
119 * @param new_mask The mask to use when matching against the key.
120 * @return Whether the current Node was advanced.
123 goesAfter(Node **parent, Node *kid, Key key, Key new_mask)
125 if (kid && kid->matches(key) && (kid->mask & new_mask) == kid->mask) {
134 * A utility method which extends a mask value one more bit towards the
135 * lsb. This is almost just a signed right shift, except that the shifted
136 * in bits are technically undefined. This is also slightly complicated by
138 * @param orig The original mask to extend.
139 * @return The extended mask.
144 // Just in case orig was 0.
145 const Key msb = ULL(1) << (MaxBits - 1);
146 return orig | (orig >> 1) | msb;
150 * Method which looks up the Handle corresponding to a particular key. This
151 * is useful if you want to delete the Handle corresponding to a key since
152 * the "remove" function takes a Handle as its argument.
153 * @param key The key to look up.
154 * @return The first Handle matching this key, or NULL if none was found.
157 lookupHandle(Key key)
164 if (node->kids[0] && node->kids[0]->matches(key))
165 node = node->kids[0];
166 else if (node->kids[1] && node->kids[1]->matches(key))
167 node = node->kids[1];
177 * Method which inserts a key/value pair into the trie.
178 * @param key The key which can later be used to look up this value.
179 * @param width How many bits of the key (from msb) should be used.
180 * @param val A pointer to the value to store in the trie.
181 * @return A Handle corresponding to this value.
184 insert(Key key, unsigned width, Value *val)
186 // Build a mask which masks off all the bits we don't care about.
187 Key new_mask = ~(Key)0;
189 new_mask <<= (MaxBits - width);
190 // Use it to tidy up the key.
193 // Walk past all the nodes this new node will be inserted after. They
194 // can be ignored for the purposes of this function.
196 while (goesAfter(&node, node->kids[0], key, new_mask) ||
197 goesAfter(&node, node->kids[1], key, new_mask))
201 Key cur_mask = node->mask;
202 // If we're already where the value needs to be...
203 if (cur_mask == new_mask) {
204 assert(!node->value);
209 for (unsigned int i = 0; i < 2; i++) {
210 Node *&kid = node->kids[i];
213 // No kid. Add a new one.
214 new_node = new Node(key, new_mask, val);
215 new_node->parent = node;
220 // Walk down the leg until something doesn't match or we run out
225 last_mask = cur_mask;
226 cur_mask = extendMask(cur_mask);
227 done = ((key & cur_mask) != (kid->key & cur_mask)) ||
228 last_mask == new_mask;
230 cur_mask = last_mask;
232 // If this isn't the right leg to go down at all, skip it.
233 if (cur_mask == node->mask)
236 // At the point we walked to above, add a new node.
237 new_node = new Node(key, cur_mask, NULL);
238 new_node->parent = node;
239 kid->parent = new_node;
240 new_node->kids[0] = kid;
243 // If we ran out of bits, the value goes right here.
244 if (cur_mask == new_mask) {
245 new_node->value = val;
249 // Still more bits to deal with, so add a new node for that path.
250 new_node = new Node(key, new_mask, val);
251 new_node->parent = kid;
252 kid->kids[1] = new_node;
256 panic("Reached the end of the Trie insert function!\n");
261 * Method which looks up the Value corresponding to a particular key.
262 * @param key The key to look up.
263 * @return The first Value matching this key, or NULL if none was found.
268 Node *node = lookupHandle(key);
276 * Method to delete a value from the trie.
277 * @param node A Handle to remove.
278 * @return The Value pointer from the removed entry.
281 remove(Handle handle)
284 Value *val = node->value;
291 panic("Trie: Can't remove root node.\n");
293 Node *parent = node->parent;
295 // If there's a kid, fix up it's parent pointer.
297 node->kids[0]->parent = parent;
298 // Figure out which kid we are, and update our parent's pointers.
299 if (parent->kids[0] == node)
300 parent->kids[0] = node->kids[0];
301 else if (parent->kids[1] == node)
302 parent->kids[1] = node->kids[0];
304 panic("Trie: Inconsistent parent/kid relationship.\n");
305 // Make sure if the parent only has one kid, it's kid[0].
306 if (parent->kids[1] && !parent->kids[0]) {
307 parent->kids[0] = parent->kids[1];
308 parent->kids[1] = NULL;
311 // If the parent has less than two kids and no cargo and isn't the
312 // root, delete it too.
313 if (!parent->kids[1] && !parent->value && parent->parent)
320 * Method to lookup a value from the trie and then delete it.
321 * @param key The key to look up and then remove.
322 * @return The Value pointer from the removed entry, if any.
327 Handle handle = lookupHandle(key);
330 return remove(handle);
334 * A method which removes all key/value pairs from the trie. This is more
335 * efficient than trying to remove elements individually.
344 * A debugging method which prints the contents of this trie.
345 * @param title An identifying title to put in the dump header.
348 dump(const char *title)
350 cprintf("**************************************************\n");
351 cprintf("*** Start of Trie: %s\n", title);
352 cprintf("*** (parent, me, key, mask, value pointer)\n");
353 cprintf("**************************************************\n");