rbtree.c

   1 /*
   2  * rbtree.c
   3  *
   4  * Simple implementation of a left-leaning red-black tree with 64-bit
   5  * integer keys.  The search operation will return the highest node <=
   6  * the key; only search, insert, and full-tree deletion is supported,
   7  * but additional standard llrbtree operations can be coded up at will.
   8  *
   9  * See http://www.cs.princeton.edu/~rs/talks/LLRB/RedBlack.pdf for
  10  * information about left-leaning red-black trees.
  11  */
  12
  13 #include "rbtree.h"
  14 #include "nasmlib.h"
  15
  16 const struct rbtree *rb_search(const struct rbtree *tree, uint64_t key)
  17 {
  18     const struct rbtree *best = NULL;
  19
  20     while (tree) {
  21         if (tree->key == key)
  22             return tree;
  23         else if (tree->key > key)
  24             tree = tree->left;
  25         else {
  26             best = tree;
  27             tree = tree->right;
  28         }
  29     }
  30     return best;
  31 }
  32
  33 static bool is_red(struct rbtree *h)
  34 {
  35     return h && h->red;
  36 }
  37
  38 static struct rbtree *rotate_left(struct rbtree *h)
  39 {
  40     struct rbtree *x = h->right;
  41     h->right = x->left;
  42     x->left = h;
  43     x->red = x->left->red;
  44     x->left->red = true;
  45     return x;
  46 }
  47
  48 static struct rbtree *rotate_right(struct rbtree *h)
  49 {
  50     struct rbtree *x = h->left;
  51     h->left = x->right;
  52     x->right = h;
  53     x->red = x->right->red;
  54     x->right->red = true;
  55     return x;
  56 }
  57
  58 static void color_flip(struct rbtree *h)
  59 {
  60     h->red = !h->red;
  61     h->left->red = !h->left->red;
  62     h->right->red = !h->right->red;
  63 }
  64
  65 struct rbtree *rb_insert(struct rbtree *tree, uint64_t key, void *data)
  66 {
  67     if (!tree) {
  68         struct rbtree *node = nasm_malloc(sizeof *node);
  69
  70         node->key   = key;
  71         node->data  = data;
  72         node->red   = true;
  73         return node;
  74     }
  75
  76     if (is_red(tree->left) && is_red(tree->right))
  77         color_flip(tree);
  78
  79     if (key < tree->key)
  80         tree->left = rb_insert(tree->left, key, data);
  81     else
  82         tree->right = rb_insert(tree->right, key, data);
  83
  84     if (is_red(tree->right))
  85         tree = rotate_left(tree);
  86
  87     if (is_red(tree->left) && is_red(tree->left->left))
  88         tree = rotate_right(tree);
  89
  90     return tree;
  91 }
  92
  93 void rb_free(struct rbtree *tree)
  94 {
  95     if (tree) {
  96         rb_free(tree->left);
  97         rb_free(tree->right);
  98         nasm_free(tree);
  99     }
 100 }