Left-leaning red-black tree data structure

Implement library functions for "left-leaning red-black trees" with
uint64_t keys.  This is meant for looking up symbols by address in the
backends that need to do so, e.g. ELF.

A good question is if there is a better way to do this, that recovers
the original symbol, but that's a future issue.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 100 insertions, 0 deletions

diff --git a/rbtree.c b/rbtree.c
new file mode 100644
index 00000000..adf2b8b4
--- /dev/null
+++ b/rbtree.c
@@ -0,0 +1,100 @@
+/*
+ * rbtree.c
+ *
+ * Simple implementation of a left-leaning red-black tree with 64-bit
+ * integer keys.  The search operation will return the highest node <=
+ * the key; only search, insert, and full-tree deletion is supported,
+ * but additional standard llrbtree operations can be coded up at will.
+ *
+ * See http://www.cs.princeton.edu/~rs/talks/LLRB/RedBlack.pdf for
+ * information about left-leaning red-black trees.
+ */
+
+#include "rbtree.h"
+#include "nasmlib.h"
+
+const struct rbtree *rb_search(const struct rbtree *tree, uint64_t key)
+{
+    const struct rbtree *best = NULL;
+
+    while (tree) {
+	if (tree->key == key)
+	    return tree;
+	else if (tree->key > key)
+	    tree = tree->left;
+	else {
+	    best = tree;
+	    tree = tree->right;
+	}
+    }
+    return best;
+}
+
+static bool is_red(struct rbtree *h)
+{
+    return h && h->red;
+}
+
+static struct rbtree *rotate_left(struct rbtree *h)
+{
+    struct rbtree *x = h->right;
+    h->right = x->left;
+    x->left = h;
+    x->red = x->left->red;
+    x->left->red = true;
+    return x;
+}
+
+static struct rbtree *rotate_right(struct rbtree *h)
+{
+    struct rbtree *x = h->left;
+    h->left = x->right;
+    x->right = h;
+    x->red = x->right->red;
+    x->right->red = true;
+    return x;
+}
+
+static void color_flip(struct rbtree *h)
+{
+    h->red = !h->red;
+    h->left->red = !h->left->red;
+    h->right->red = !h->right->red;
+}
+
+struct rbtree *rb_insert(struct rbtree *tree, uint64_t key, void *data)
+{
+    if (!tree) {
+	struct rbtree *node = nasm_malloc(sizeof *node);
+    
+	node->key   = key;
+	node->data  = data;
+	node->red   = true;
+	return node;
+    }
+
+    if (is_red(tree->left) && is_red(tree->right))
+	color_flip(tree);
+
+    if (key < tree->key)
+	tree->left = rb_insert(tree->left, key, data);
+    else
+	tree->right = rb_insert(tree->right, key, data);
+
+    if (is_red(tree->right))
+	tree = rotate_left(tree);
+
+    if (is_red(tree->left) && is_red(tree->left->left))
+	tree = rotate_right(tree);
+
+    return tree;
+}
+
+void rb_free(struct rbtree *tree)
+{
+    if (tree) {
+	rb_free(tree->left);
+	rb_free(tree->right);
+	nasm_free(tree);
+    }
+}