start implementing generic b-tree interface

2025-01-30 21:51:00 +00:00
parent 6a0e3b41f6
commit 8d2d937861
2 changed files with 263 additions and 5 deletions
--- a/src/b-tree.c
+++ b/src/b-tree.c
@@ -0,0 +1,247 @@
+#include <blue/core/queue.h>
+
+#include "b-tree.h"
+
+#define SWAP(type, x, y)                                                       \
+	do {                                                                   \
+		type tmp = x;                                                  \
+		x = y;                                                         \
+		y = tmp;                                                       \
+	} while (0)
+
+struct cache_entry {
+	int c_allocated;
+	b_queue_entry c_entry;
+	/* ... node data here ... */
+};
+
+static b_tree_node *cache_alloc_node(struct b_tree *tree)
+{
+	b_queue_iterator it = { 0 };
+	b_queue_foreach (&it, &tree->tree_cache) {
+		struct cache_entry *e = b_unbox(struct cache_entry, it.entry, c_entry);
+		if (!e->c_allocated) {
+			e->c_allocated = 1;
+			return (b_tree_node *)(e + 1);
+		}
+	}
+
+	struct cache_entry *e = malloc(sizeof *e + tree->tree_ops->node_size);
+	if (!e) {
+		return NULL;
+	}
+
+	memset(e, 0x0, sizeof *e);
+	e->c_allocated = 1;
+	e->c_entry = B_QUEUE_ENTRY_INIT;
+
+	b_queue_push_back(&tree->tree_cache, &e->c_entry);
+
+	return (b_tree_node *)(e + 1);
+}
+
+static void cache_free_node(struct b_tree *tree, b_tree_node *node)
+{
+	struct cache_entry *e = (struct cache_entry *)((unsigned char *)node - sizeof *e);
+	e->c_allocated = 0;
+}
+
+void b_tree_init(struct b_tree *tree, const struct b_tree_ops *ops, unsigned int order)
+{
+	memset(tree, 0x0, sizeof *tree);
+	tree->tree_ops = ops;
+	tree->tree_order = order;
+}
+
+static int node_read(struct b_tree *tree, long id, b_tree_node *out)
+{
+
+}
+
+static unsigned long node_get_nr_entries(struct b_tree *tree, b_tree_node *node)
+{
+	return tree->tree_ops->node_get_nr_entries(node);
+}
+
+static long node_get_child(struct b_tree *tree, b_tree_node *node, unsigned long index)
+{
+	return tree->tree_ops->node_get_child(node, index);
+}
+
+static void node_set_child(struct b_tree *tree, b_tree_node *node, unsigned long index, long ptr)
+{
+	tree->tree_ops->node_set_child(node, index, ptr);
+}
+
+static b_tree_node_entry node_get_entry(struct b_tree *tree, b_tree_node *node, unsigned long index)
+{
+	return tree->tree_ops->node_get_entry(node, index);
+}
+
+static int node_is_leaf(struct b_tree *tree, b_tree_node *node)
+{
+	long first_child = node_get_child(tree, node, 0);
+	return first_child == B_TREE_INVALID_PTR;
+}
+
+static void node_init(struct b_tree *tree, b_tree_node *out)
+{
+	memset(out, 0x0, tree->tree_ops->node_size);
+	for (unsigned int i = 0; i < tree->tree_order; i++) {
+		node_set_child(tree, out, i, B_TREE_INVALID_PTR);
+	}
+}
+
+static int entry_compare(struct b_tree *tree, b_tree_node_entry *a, b_tree_node_entry *b)
+{
+	return tree->tree_ops->entry_compare(a, b);
+}
+
+int b_tree_put(struct b_tree *tree, const b_tree_node_entry *to_put)
+{
+	int depth = 0;
+
+	long current_id = tree->tree_root;
+	long next_id = -1;
+	
+	b_tree_node *current = cache_alloc_node(tree);
+	b_tree_node *next = cache_alloc_node(tree);
+
+	int err = node_read(tree, current_id, current);
+
+	if (err != 0) {
+		return err;
+	}
+
+	unsigned long nr_entries = node_get_nr_entries(tree, current);
+
+	if (nr_entries == tree->tree_order - 1) {
+		/* root node is full. split it pre-emptively. */
+		b_tree_node *a = next;
+		b_tree_node *b = cache_alloc_node(tree);
+		
+		node_init(tree, a);
+		node_init(tree, b);
+
+		int median = nr_entries / 2;
+
+		node_move_entries(current, &a, 0, 0, median);
+		node_move_entries(current, &b, 1, 0, median);
+
+		node_move_children(current, &a, 0, 0, median + 1);
+		node_move_children(current, &b, median + 1, 0, median + 1);
+
+		int a_index = tree_alloc_id(tree);
+		node_write(tree, a_index, a);
+
+		int b_index = tree_alloc_id(tree);
+		node_write(tree, b_index, b);
+
+		node_set_child(tree, current, 0, a_index);
+		node_set_child(tree, current, 1, b_index);
+
+		node_write(tree, current_id, current);
+
+		cache_free_node(tree, b);
+	}
+
+	bool leaf = node_is_leaf(tree, current);
+
+	while (!leaf) {
+		unsigned int i;
+		bool found_bigger_key = false;
+
+		nr_entries = node_get_nr_entries(tree, current);
+		next_id = node_get_child(tree, current, nr_entries);
+
+		for (i = 0; i < nr_entries; i++) {
+			b_tree_node_entry *entry = node_get_entry(tree, current, i);
+			int cmp = entry_compare(tree, entry, to_put);
+
+			if (cmp == 1) {
+				next_id = node_get_child(tree, current, i);
+				break;
+			}
+		}
+
+		err = node_read(tree, next_id, next);
+		if (err != 0) {
+			return err;
+		}
+
+		nr_entries = node_get_nr_entries(tree, next);
+		if (nr_entries < tree->tree_order - 1) {
+			/* swap current and next pointers. */
+			SWAP(b_tree_node *, current, next);
+			current_id = next_id;
+
+			leaf = node_is_leaf(tree, current);
+
+			depth++;
+			continue;
+		}
+
+		/* this node is full, split it. */
+
+		/* half the nodes from `next` will be moved into `n3`. the other
+		   half will stay put. the median entry will be moved to
+		   `current`.
+
+		   `n3` will become the right sibling of `next` */
+		b_tree_node *n3 = cache_alloc_node(tree);
+		node_init(tree, n3);
+
+		bool n3_is_next = false;
+		nr_entries = node_get_nr_entries(tree, next);
+		int median = nr_entries / 2;
+		b_tree_node_entry *median_node = node_get_entry(tree, next, median);
+		int cmp = entry_compare(tree, median_node, to_put);
+		if (cmp == -1) {
+			// median++;
+			n3_is_next = true;
+		}
+
+#if 0
+		node_move_entries(
+			next,
+			&n3,
+			median + 1,
+			0,
+			nr_entries - median - 1);
+		node_move_children(
+			next,
+			&n3,
+			median + 1,
+			0,
+			nr_entries - median);
+		int index = node_put(current, &next->entries[median]);
+		memset(&next->entries[median], 0x00, sizeof(struct entry));
+		next->nr_entries--;
+		node_shift_children(current, index + 1, 1);
+
+		int n3_id = tree_alloc_id(tree);
+
+		current->children[index + 1] = n3_id;
+		node_write(tree->fp, current_id, current);
+		node_write(tree->fp, next_id, next);
+		node_write(tree->fp, n3_id, &n3);
+
+		if (n3_is_next) {
+			memcpy(current, &n3, sizeof n3);
+			current_id = n3_id;
+		}
+		else {
+			SWAP(struct node *, current, next);
+			current_id = next_id;
+		}
+
+		depth++;
+		leaf = node_is_leaf(current);
+#endif
+	}
+#if 0
+	node_put(current, e);
+	node_write(tree->fp, current_id, current);
+#endif
+	return 0;
+}
--- a/src/b-tree.h
+++ b/src/b-tree.h
@@ -2,6 +2,9 @@
 #define B_TREE_H_

 #include <stddef.h>
+#include <blue/core/queue.h>
+
+#define B_TREE_INVALID_PTR -1

 struct b_tree;
 typedef void *b_tree_node;
@@ -11,19 +14,27 @@ struct b_tree_ops {
 	size_t node_size;
 	size_t entry_size;

-	int (*tree_get_node)(struct b_tree *, int, void *);
-	int (*tree_put_node)(struct b_tree *, int, void *);
+	int (*tree_get_node)(struct b_tree *, long, void *);
+	int (*tree_put_node)(struct b_tree *, long, void *);
 	int (*tree_alloc_node)(struct b_tree *);

-	int (*node_get_nr_entries)(b_tree_node *);
-	b_tree_node_entry *(*node_get_entry)(b_tree_node *, int);
-	int (*node_get_child)(b_tree_node *, int);
+	long (*node_get_nr_entries)(b_tree_node *);
+	b_tree_node_entry *(*node_get_entry)(b_tree_node *, unsigned long);
+	void (*node_set_entry)(b_tree_node *, int, const b_tree_node_entry *);
+	long (*node_get_child)(b_tree_node *, unsigned long);
+	int (*node_set_child)(b_tree_node *, unsigned long, long);

 	int (*entry_compare)(b_tree_node_entry *, b_tree_node_entry *);
 };

 struct b_tree {
 	const struct b_tree_ops *tree_ops;
+	b_queue tree_cache;
+	unsigned int tree_order;
+	long tree_root;
 };

+extern void b_tree_init(struct b_tree *tree, const struct b_tree_ops *ops, unsigned int order);
+extern int b_tree_put(struct b_tree *tree, const b_tree_node_entry *entry);
+
 #endif