LibC: Implement POSIX binary search trees

I used RB tree for this. The implementation is based on the code on wikipedia about RB trees.
2026-07-20 04:07:23 +03:00
parent 658e74b507
commit 2a3eca5b36
3 changed files with 306 additions and 12 deletions
@@ -32,6 +32,7 @@ set(LIBC_SOURCES
 	regex.cpp
 	scanf_impl.cpp
 	sched.cpp
+	search.cpp
 	semaphore.cpp
 	setjmp.cpp
 	signal.cpp
@@ -1,7 +1,7 @@
 #ifndef _SEARCH_H
 #define _SEARCH_H 1

-// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/search.h.html
+// https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/search.h.html

 #include <sys/cdefs.h>

@@ -19,17 +19,25 @@ typedef struct
 typedef enum { FIND, ENTER } ACTION;
 typedef enum { preorder, postorder, endorder, leaf } VISIT;

-int		hcreate(size_t nel);
-void	hdestroy(void);
-ENTRY*	hsearch(ENTRY item, ACTION action);
-void	insque(void* element, void* pred);
-void*	lfind(const void* key, const void* base, size_t* nelp, size_t width, int (*compar)(const void*, const void*));
-void*	lsearch(const void* key, void* base, size_t* nelp, size_t width, int (*compar)(const void*, const void*));
-void	remque(void* element);
-void*	tdelete(const void* __restrict key, void** __restrict rootp, int(*compar)(const void*, const void*));
-void*	tfind(const void* key, void* const* rootp, int(*compar)(const void*, const void*));
-void*	tsearch(const void* key, void** rootp, int(*compar)(const void*, const void*));
-void	twalk(const void* root, void (*action)(const void*, VISIT, int));
+// NOTE: POSIX requires posix_tnode to be void but
+//       defining an internal type avoids casting
+#ifdef __is_libc
+typedef struct __posix_tnode posix_tnode;
+#else
+typedef void posix_tnode;
+#endif
+
+int          hcreate(size_t nel);
+void         hdestroy(void);
+ENTRY*       hsearch(ENTRY item, ACTION action);
+void         insque(void* element, void* pred);
+void*        lfind(const void* key, const void* base, size_t* nelp, size_t width, int (*compar)(const void*, const void*));
+void*        lsearch(const void* key, void* base, size_t* nelp, size_t width, int (*compar)(const void*, const void*));
+void         remque(void* element);
+void*        tdelete(const void* __restrict key, posix_tnode** __restrict rootp, int (*compar)(const void*, const void*));
+posix_tnode* tfind(const void* key, posix_tnode* const* rootp, int (*compar)(const void*, const void*));
+posix_tnode* tsearch(const void* key, posix_tnode** rootp, int (*compar)(const void*, const void*));
+void         twalk(const posix_tnode* root, void (*action)(const posix_tnode*, VISIT, int));

 __END_DECLS

@@ -0,0 +1,285 @@
+#include <search.h>
+#include <stdlib.h>
+
+// RB Tree implementation based on the code in wikipedia https://en.wikipedia.org/wiki/Red%E2%80%93black_tree
+
+struct __posix_tnode
+{
+	const void* key;
+	posix_tnode* parent;
+	posix_tnode* children[2];
+	enum { RED, BLACK } color;
+};
+
+posix_tnode* tfind(const void* key, posix_tnode* const* rootp, int (*compar)(const void*, const void*))
+{
+	if (*rootp == nullptr)
+		return nullptr;
+
+	posix_tnode* node = *rootp;
+	while (node)
+	{
+		const int result = compar(key, node->key);
+		if (result == 0)
+			return node;
+		node = node->children[result > 0];
+	}
+
+	return nullptr;
+}
+
+static posix_tnode* _trotate(posix_tnode** root, posix_tnode* node, int dir)
+{
+	posix_tnode* old_parent = node->parent;
+	posix_tnode* new_root   = node->children[1 - dir];
+	posix_tnode* new_child  = new_root->children[dir];
+
+	node->children[1 - dir] = new_child;
+
+	if (new_child)
+		new_child->parent = node;
+
+	new_root->children[dir] = node;
+
+	new_root->parent = old_parent;
+	node->parent = new_root;
+	if (old_parent)
+		old_parent->children[node == old_parent->children[1]] = new_root;
+	else
+		*root = new_root;
+
+	return new_root;
+}
+
+static void _tinsert(posix_tnode** root, posix_tnode* node, posix_tnode* parent, int dir)
+{
+	node->color = posix_tnode::RED;
+	node->parent = parent;
+
+	if (!parent)
+	{
+		*root = node;
+		return;
+	}
+
+	parent->children[dir] = node;
+
+	do {
+		if (parent->color == posix_tnode::BLACK)
+			return;
+
+		posix_tnode* grandparent = parent->parent;
+		if (!grandparent)
+		{
+			parent->color = posix_tnode::BLACK;
+			return;
+		}
+
+		dir = (parent == grandparent->children[1]);
+
+		posix_tnode* uncle = grandparent->children[1 - dir];
+		if (!uncle || uncle->color == posix_tnode::BLACK)
+		{
+			if (node == parent->children[1 - dir])
+			{
+				_trotate(root, parent, dir);
+				node = parent;
+				parent = grandparent->children[dir];
+			}
+
+			_trotate(root, grandparent, 1 - dir);
+			parent->color = posix_tnode::BLACK;
+			grandparent->color = posix_tnode::RED;
+			return;
+		}
+
+		parent->color = posix_tnode::BLACK;
+		uncle->color = posix_tnode::BLACK;
+		grandparent->color = posix_tnode::RED;
+		node = grandparent;
+	} while ((parent = node->parent));
+}
+
+posix_tnode* tsearch(const void* key, posix_tnode** root, int (*compar)(const void*, const void*))
+{
+	posix_tnode* parent = nullptr;
+	posix_tnode* node = *root;
+	int dir = 0;
+
+	while (node)
+	{
+		const int result = compar(key, node->key);
+		if (result == 0)
+			return node;
+		parent = node;
+		dir = (result > 0);
+		node = node->children[dir];
+	}
+
+	node = static_cast<posix_tnode*>(malloc(sizeof(posix_tnode)));
+	if (node == nullptr)
+		return nullptr;
+
+	*node = {
+		.key = key,
+		.parent = nullptr,
+		.children = {},
+		.color = posix_tnode::RED,
+	};
+
+	_tinsert(root, node, parent, dir);
+
+	return node;
+}
+
+static void _tremove_black_leaf(posix_tnode** __restrict root, posix_tnode* node)
+{
+	const auto case6 = [&](posix_tnode* parent, posix_tnode* sibling, posix_tnode* far_nephew, int dir) -> bool {
+		_trotate(root, parent, dir);
+		sibling->color = parent->color;
+		parent->color = posix_tnode::BLACK;
+		far_nephew->color = posix_tnode::BLACK;
+		return true;
+	};
+
+	const auto case5 = [&](posix_tnode* parent, posix_tnode* sibling, posix_tnode* near_nephew, int dir) -> bool {
+		_trotate(root, sibling, 1 - dir);
+		sibling->color = posix_tnode::RED;
+		near_nephew->color = posix_tnode::BLACK;
+		case6(parent, near_nephew, sibling, dir);
+		return true;
+	};
+
+	const auto try_case56 = [&](posix_tnode* parent, posix_tnode* sibling, int dir) -> bool {
+		if (posix_tnode* far_nephew  = sibling->children[1 - dir]; far_nephew  && far_nephew->color  == posix_tnode::RED)
+			return case6(parent, sibling, far_nephew, dir);
+		if (posix_tnode* near_nephew = sibling->children[    dir]; near_nephew && near_nephew->color == posix_tnode::RED)
+			return case5(parent, sibling, near_nephew, dir);
+		return false;
+	};
+
+	posix_tnode* parent = node->parent;
+
+	int dir = (node == parent->children[1]);
+
+	parent->children[dir] = nullptr;
+
+	for (;;)
+	{
+		posix_tnode* sibling = parent->children[1 - dir];
+
+		if (sibling->color == posix_tnode::RED)
+		{
+			posix_tnode* near_nephew = sibling->children[dir];
+
+			_trotate(root, parent, dir);
+			parent->color = posix_tnode::RED;
+			sibling->color = posix_tnode::BLACK;
+			sibling = near_nephew;
+
+			if (try_case56(parent, sibling, dir))
+				return;
+
+			sibling->color = posix_tnode::RED;
+			parent->color = posix_tnode::BLACK;
+			return;
+		}
+
+		if (try_case56(parent, sibling, dir))
+			return;
+
+		if (parent->color == posix_tnode::RED)
+		{
+			sibling->color = posix_tnode::RED;
+			parent->color = posix_tnode::BLACK;
+			return;
+		}
+
+		sibling->color = posix_tnode::RED;
+
+		node = parent;
+		parent = node->parent;
+		if (parent == nullptr)
+			return;
+
+		dir = (node == parent->children[1]);
+	}
+}
+
+void* tdelete(const void* __restrict key, posix_tnode** __restrict root, int (*compar)(const void*, const void*))
+{
+	posix_tnode* node = tfind(key, root, compar);
+	if (node == nullptr)
+		return nullptr;
+
+	// The tdelete() function shall return a pointer to the parent of the deleted node, or an unspecified non-null pointer
+	// if the deleted node was the root node, or a null pointer if the node is not found.
+	static posix_tnode dummy {};
+	posix_tnode* return_value = node->parent ? node->parent : &dummy;
+
+	if (node->children[0] && node->children[1])
+	{
+		posix_tnode* succ = node->children[1];
+		while (succ->children[0])
+			succ = succ->children[0];
+		node->key = succ->key;
+		node = succ;
+	}
+
+	posix_tnode* parent = node->parent;
+	posix_tnode* child = node->children[0]
+		? node->children[0]
+		: node->children[1];
+
+	if (parent == nullptr || child)
+	{
+		posix_tnode* parent = node->parent;
+
+		if (child)
+		{
+			child->parent = parent;
+			child->color = posix_tnode::BLACK;
+		}
+
+		if (parent == nullptr)
+			*root = child;
+		else
+		{
+			int dir = (node == parent->children[1]);
+			parent->children[dir] = child;
+		}
+	}
+	else if (node->color == posix_tnode::RED)
+	{
+		int dir = (node == parent->children[1]);
+		parent->children[dir] = nullptr;
+	}
+	else
+	{
+		_tremove_black_leaf(root, node);
+	}
+
+	free(node);
+
+	return return_value;
+}
+
+static void _twalk(const posix_tnode* node, void (*action)(const posix_tnode*, VISIT, int), int depth)
+{
+	if (!node->children[0] && !node->children[1])
+		return action(node, leaf, depth);
+	action(node, preorder, depth);
+	if (node->children[0])
+		_twalk(node->children[0], action, depth + 1);
+	action(node, postorder, depth);
+	if (node->children[1])
+		_twalk(node->children[1], action, depth + 1);
+	action(node, endorder, depth);
+}
+
+void twalk(const posix_tnode* root, void (*action)(const posix_tnode*, VISIT, int))
+{
+	if (root == nullptr)
+		return;
+	_twalk(root, action, 0);
+}