122 lines
3.4 KiB
C
122 lines
3.4 KiB
C
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#include "rotatingtree.h"
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#define KEY_LOWER_THAN(key1, key2) ((char*)(key1) < (char*)(key2))
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/* The randombits() function below is a fast-and-dirty generator that
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* is probably irregular enough for our purposes. Note that it's biased:
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* I think that ones are slightly more probable than zeroes. It's not
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* important here, though.
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*/
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static unsigned int random_value = 1;
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static unsigned int random_stream = 0;
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static int
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randombits(int bits)
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{
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int result;
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if (random_stream < (1U << bits)) {
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random_value *= 1082527;
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random_stream = random_value;
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}
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result = random_stream & ((1<<bits)-1);
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random_stream >>= bits;
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return result;
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}
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/* Insert a new node into the tree.
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(*root) is modified to point to the new root. */
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void
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RotatingTree_Add(rotating_node_t **root, rotating_node_t *node)
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{
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while (*root != NULL) {
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if (KEY_LOWER_THAN(node->key, (*root)->key))
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root = &((*root)->left);
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else
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root = &((*root)->right);
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}
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node->left = NULL;
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node->right = NULL;
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*root = node;
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}
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/* Locate the node with the given key. This is the most complicated
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function because it occasionally rebalances the tree to move the
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resulting node closer to the root. */
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rotating_node_t *
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RotatingTree_Get(rotating_node_t **root, void *key)
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{
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if (randombits(3) != 4) {
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/* Fast path, no rebalancing */
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rotating_node_t *node = *root;
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while (node != NULL) {
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if (node->key == key)
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return node;
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if (KEY_LOWER_THAN(key, node->key))
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node = node->left;
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else
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node = node->right;
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}
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return NULL;
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}
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else {
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rotating_node_t **pnode = root;
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rotating_node_t *node = *pnode;
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rotating_node_t *next;
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int rotate;
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if (node == NULL)
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return NULL;
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while (1) {
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if (node->key == key)
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return node;
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rotate = !randombits(1);
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if (KEY_LOWER_THAN(key, node->key)) {
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next = node->left;
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if (next == NULL)
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return NULL;
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if (rotate) {
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node->left = next->right;
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next->right = node;
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*pnode = next;
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}
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else
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pnode = &(node->left);
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}
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else {
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next = node->right;
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if (next == NULL)
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return NULL;
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if (rotate) {
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node->right = next->left;
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next->left = node;
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*pnode = next;
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}
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else
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pnode = &(node->right);
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}
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node = next;
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}
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}
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}
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/* Enumerate all nodes in the tree. The callback enumfn() should return
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zero to continue the enumeration, or non-zero to interrupt it.
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A non-zero value is directly returned by RotatingTree_Enum(). */
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int
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RotatingTree_Enum(rotating_node_t *root, rotating_tree_enum_fn enumfn,
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void *arg)
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{
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int result;
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rotating_node_t *node;
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while (root != NULL) {
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result = RotatingTree_Enum(root->left, enumfn, arg);
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if (result != 0) return result;
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node = root->right;
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result = enumfn(root, arg);
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if (result != 0) return result;
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root = node;
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}
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return 0;
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}
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