Line data    Source code

       1             : #include "rotatingtree.h"
       2             : 
       3             : #define KEY_LOWER_THAN(key1, key2)  ((char*)(key1) < (char*)(key2))
       4             : 
       5             : /* The randombits() function below is a fast-and-dirty generator that
       6             :  * is probably irregular enough for our purposes.  Note that it's biased:
       7             :  * I think that ones are slightly more probable than zeroes.  It's not
       8             :  * important here, though.
       9             :  */
      10             : 
      11             : static unsigned int random_value = 1;
      12             : static unsigned int random_stream = 0;
      13             : 
      14             : static int
      15           0 : randombits(int bits)
      16             : {
      17             :     int result;
      18           0 :     if (random_stream < (1U << bits)) {
      19           0 :         random_value *= 1082527;
      20           0 :         random_stream = random_value;
      21             :     }
      22           0 :     result = random_stream & ((1<<bits)-1);
      23           0 :     random_stream >>= bits;
      24           0 :     return result;
      25             : }
      26             : 
      27             : 
      28             : /* Insert a new node into the tree.
      29             :    (*root) is modified to point to the new root. */
      30             : void
      31           0 : RotatingTree_Add(rotating_node_t **root, rotating_node_t *node)
      32             : {
      33           0 :     while (*root != NULL) {
      34           0 :         if (KEY_LOWER_THAN(node->key, (*root)->key))
      35           0 :             root = &((*root)->left);
      36             :         else
      37           0 :             root = &((*root)->right);
      38             :     }
      39           0 :     node->left = NULL;
      40           0 :     node->right = NULL;
      41           0 :     *root = node;
      42           0 : }
      43             : 
      44             : /* Locate the node with the given key.  This is the most complicated
      45             :    function because it occasionally rebalances the tree to move the
      46             :    resulting node closer to the root. */
      47             : rotating_node_t *
      48           0 : RotatingTree_Get(rotating_node_t **root, void *key)
      49             : {
      50           0 :     if (randombits(3) != 4) {
      51             :         /* Fast path, no rebalancing */
      52           0 :         rotating_node_t *node = *root;
      53           0 :         while (node != NULL) {
      54           0 :             if (node->key == key)
      55           0 :                 return node;
      56           0 :             if (KEY_LOWER_THAN(key, node->key))
      57           0 :                 node = node->left;
      58             :             else
      59           0 :                 node = node->right;
      60             :         }
      61           0 :         return NULL;
      62             :     }
      63             :     else {
      64           0 :         rotating_node_t **pnode = root;
      65           0 :         rotating_node_t *node = *pnode;
      66             :         rotating_node_t *next;
      67             :         int rotate;
      68           0 :         if (node == NULL)
      69           0 :             return NULL;
      70             :         while (1) {
      71           0 :             if (node->key == key)
      72           0 :                 return node;
      73           0 :             rotate = !randombits(1);
      74           0 :             if (KEY_LOWER_THAN(key, node->key)) {
      75           0 :                 next = node->left;
      76           0 :                 if (next == NULL)
      77           0 :                     return NULL;
      78           0 :                 if (rotate) {
      79           0 :                     node->left = next->right;
      80           0 :                     next->right = node;
      81           0 :                     *pnode = next;
      82             :                 }
      83             :                 else
      84           0 :                     pnode = &(node->left);
      85             :             }
      86             :             else {
      87           0 :                 next = node->right;
      88           0 :                 if (next == NULL)
      89           0 :                     return NULL;
      90           0 :                 if (rotate) {
      91           0 :                     node->right = next->left;
      92           0 :                     next->left = node;
      93           0 :                     *pnode = next;
      94             :                 }
      95             :                 else
      96           0 :                     pnode = &(node->right);
      97             :             }
      98           0 :             node = next;
      99           0 :         }
     100             :     }
     101             : }
     102             : 
     103             : /* Enumerate all nodes in the tree.  The callback enumfn() should return
     104             :    zero to continue the enumeration, or non-zero to interrupt it.
     105             :    A non-zero value is directly returned by RotatingTree_Enum(). */
     106             : int
     107           0 : RotatingTree_Enum(rotating_node_t *root, rotating_tree_enum_fn enumfn,
     108             :                   void *arg)
     109             : {
     110             :     int result;
     111             :     rotating_node_t *node;
     112           0 :     while (root != NULL) {
     113           0 :         result = RotatingTree_Enum(root->left, enumfn, arg);
     114           0 :         if (result != 0) return result;
     115           0 :         node = root->right;
     116           0 :         result = enumfn(root, arg);
     117           0 :         if (result != 0) return result;
     118           0 :         root = node;
     119             :     }
     120           0 :     return 0;
     121             : }