AppPkg/Applications/Python/Python-2.7.2/Modules/rotatingtree.c

   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 randombits(int bits)
  16 {
  17     int result;
  18     if (random_stream < (1U << bits)) {
  19         random_value *= 1082527;
  20         random_stream = random_value;
  21     }
  22     result = random_stream & ((1<<bits)-1);
  23     random_stream >>= bits;
  24     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 RotatingTree_Add(rotating_node_t **root, rotating_node_t *node)
  32 {
  33     while (*root != NULL) {
  34         if (KEY_LOWER_THAN(node->key, (*root)->key))
  35             root = &((*root)->left);
  36         else
  37             root = &((*root)->right);
  38     }
  39     node->left = NULL;
  40     node->right = NULL;
  41     *root = node;
  42 }
  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 RotatingTree_Get(rotating_node_t **root, void *key)
  49 {
  50     if (randombits(3) != 4) {
  51         /* Fast path, no rebalancing */
  52         rotating_node_t *node = *root;
  53         while (node != NULL) {
  54             if (node->key == key)
  55                 return node;
  56             if (KEY_LOWER_THAN(key, node->key))
  57                 node = node->left;
  58             else
  59                 node = node->right;
  60         }
  61         return NULL;
  62     }
  63     else {
  64         rotating_node_t **pnode = root;
  65         rotating_node_t *node = *pnode;
  66         rotating_node_t *next;
  67         int rotate;
  68         if (node == NULL)
  69             return NULL;
  70         while (1) {
  71             if (node->key == key)
  72                 return node;
  73             rotate = !randombits(1);
  74             if (KEY_LOWER_THAN(key, node->key)) {
  75                 next = node->left;
  76                 if (next == NULL)
  77                     return NULL;
  78                 if (rotate) {
  79                     node->left = next->right;
  80                     next->right = node;
  81                     *pnode = next;
  82                 }
  83                 else
  84                     pnode = &(node->left);
  85             }
  86             else {
  87                 next = node->right;
  88                 if (next == NULL)
  89                     return NULL;
  90                 if (rotate) {
  91                     node->right = next->left;
  92                     next->left = node;
  93                     *pnode = next;
  94                 }
  95                 else
  96                     pnode = &(node->right);
  97             }
  98             node = next;
  99         }
 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 RotatingTree_Enum(rotating_node_t *root, rotating_tree_enum_fn enumfn,
 108                   void *arg)
 109 {
 110     int result;
 111     rotating_node_t *node;
 112     while (root != NULL) {
 113         result = RotatingTree_Enum(root->left, enumfn, arg);
 114         if (result != 0) return result;
 115         node = root->right;
 116         result = enumfn(root, arg);
 117         if (result != 0) return result;
 118         root = node;
 119     }
 120     return 0;
 121 }