From 3a6eda995ecfcebff3130d86ee3baeab12a41335 Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Mon, 4 Apr 2022 20:28:23 +0200
Subject: [PATCH] Typed lists for easier walking and stronger type checking

---
 lib/tlists.h | 172 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 172 insertions(+)
 create mode 100644 lib/tlists.h

diff --git a/lib/tlists.h b/lib/tlists.h
new file mode 100644
index 00000000..e1ed79ea
--- /dev/null
+++ b/lib/tlists.h
@@ -0,0 +1,172 @@
+/*
+ *	BIRD Library -- Typed Linked Lists
+ *
+ *	(c) 2022 Maria Matejka <mq@jmq.cz>
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ *
+ *
+ *	This implementation of linked lists forces its members to be
+ *	typed. On the other hand, it needs to be implemented as ugly macros to
+ *	keep the needed genericity.
+ *
+ *	Usage:
+ *	1. Include this file
+ *	2. Define the node structure
+ *	3. For every list type you need to define:
+ *	  A. #define TLIST_PREFIX and other macros
+ *	  B. Include this file once again
+ *
+ *	Macros to define:
+ *	TLIST_PREFIX:		prefix to prepend to everything generated
+ *	TLIST_TYPE:		the actual node type
+ *	TLIST_ITEM:		where the tlist structure is
+ *	TLIST_WANT_WALK:	if defined, generates a helper functions for list walking macros
+ *	TLIST_WANT_ADD_HEAD:	if defined, TLIST_PREFIX_add_head() is generated to
+ *				add an item to the beginning of the list
+ *	TLIST_WANT_ADD_TAIL:	if defined, TLIST_PREFIX_add_tail() is generated to
+ *				add an item to the end of the list
+ *
+ *	TLIST_PREFIX_rem_node() is generated always.
+ *
+ *	All these macros are #undef-ed by including this file.
+ *
+ *	Example:
+ *
+ *	#include "lib/tlists.h"
+ *	
+ *	struct foo {
+ *	  ...
+ *	  TLIST_NODE(bar, struct foo) baz;
+ *	  ...
+ *	};
+ *
+ *	#define TLIST_PREFIX  bar
+ *	#define TLIST_TYPE    struct foo
+ *	#define TLIST_ITEM    baz
+ *
+ *	#define TLIST_WANT_WALK
+ *	#define TLIST_WANT_ADD_HEAD
+ *
+ *	#include "lib/tlists.h"
+ *
+ *	...
+ *	(end of example)
+ *
+ */
+
+#ifdef _BIRD_LIB_TLISTS_H_
+# ifdef TLIST_PREFIX
+
+/* Check for mandatory arguments */
+#ifndef TLIST_TYPE
+#error "TLIST_TYPE must be defined"
+#endif
+#ifndef TLIST_ITEM
+#error "TLIST_ITEM must be defined"
+#endif
+#ifndef TLIST_PREFIX
+#error "TLIST_PREFIX must be defined"
+#endif
+
+#define TLIST_NAME(x)	MACRO_CONCAT_AFTER(TLIST_PREFIX,_##x)
+#ifndef TLIST_LIST_STRUCT
+#define TLIST_LIST_STRUCT	TLIST_NAME(list)
+#endif
+
+typedef struct TLIST_LIST_STRUCT {
+  TLIST_TYPE *first;
+  TLIST_TYPE *last;
+} TLIST_LIST_STRUCT;
+
+#ifdef TLIST_WANT_WALK
+static inline struct TLIST_NAME(node) * TLIST_NAME(node_get)(TLIST_TYPE *node)
+{ return &(node->TLIST_ITEM); }
+#endif
+
+#ifdef TLIST_WANT_ADD_HEAD
+static inline void TLIST_NAME(add_head)(TLIST_LIST_STRUCT *list, TLIST_TYPE *node)
+{
+  ASSERT_DIE(!node->TLIST_ITEM.prev && !node->TLIST_ITEM.next);
+  if (node->TLIST_ITEM.next = list->first)
+    list->first->TLIST_ITEM.prev = node;
+  else
+    list->last = node;
+  list->first = node;
+}
+#endif
+
+#ifdef TLIST_WANT_ADD_TAIL
+static inline void TLIST_NAME(add_tail)(TLIST_LIST_STRUCT *list, TLIST_TYPE *node)
+{
+  ASSERT_DIE(!node->TLIST_ITEM.prev && !node->TLIST_ITEM.next);
+  if (node->TLIST_ITEM.prev = list->last)
+    list->last->TLIST_ITEM.next = node;
+  else
+    list->first = node;
+  list->last = node;
+}
+#endif
+
+static inline void TLIST_NAME(rem_node)(TLIST_LIST_STRUCT *list, TLIST_TYPE *node)
+{
+  if (node->TLIST_ITEM.prev)
+    node->TLIST_ITEM.prev->TLIST_ITEM.next = node->TLIST_ITEM.next;
+  else
+  {
+    ASSERT_DIE(list->first == node);
+    list->first = node->TLIST_ITEM.next;
+  }
+
+  if (node->TLIST_ITEM.next)
+    node->TLIST_ITEM.next->TLIST_ITEM.prev = node->TLIST_ITEM.prev;
+  else
+  {
+    ASSERT_DIE(list->last == node);
+    list->last = node->TLIST_ITEM.prev;
+  }
+
+  node->TLIST_ITEM.next = node->TLIST_ITEM.prev = NULL;
+}
+
+#undef TLIST_PREFIX
+#undef TLIST_NAME
+#undef TLIST_LIST_STRUCT
+#undef TLIST_TYPE
+#undef TLIST_ITEM
+#undef TLIST_WANT_ADD_HEAD
+#undef TLIST_WANT_ADD_TAIL
+
+# endif
+#else
+#define _BIRD_LIB_TLISTS_H_
+
+#include "lib/macro.h"
+
+#if defined(TLIST_NAME) || defined(TLIST_PREFIX)
+#error "You should first include lib/tlists.h without requesting a TLIST"
+#endif
+
+#define TLIST_NODE(_name, _type)	struct _name##_node { _type *next; _type *prev; }
+#define TLIST_LIST(_name)		struct _name##_list 
+
+/* Use ->first and ->last to access HEAD and TAIL */
+#define THEAD(_name, _list)  (_list)->first
+#define TTAIL(_name, _list)  (_list)->last
+
+/* Walkaround macros: simple and resilient to node removal */
+#define WALK_TLIST(_name, _node, _list) \
+  for (typeof((_list)->first) _node = (_list)->first; \
+      _node; _node = _name##_node_get((_node))->next)
+
+#define WALK_TLIST_DELSAFE(_name, _node, _list) \
+  for (typeof((_list)->first) _node = (_list)->first, \
+      _helper = _node ? _name##_node_get((_list)->first)->next : NULL; \
+      _node; \
+      (_node = _helper) ? (_helper = _name##_node_get(_helper)->next) : 0)
+
+/* Empty check */
+#define EMPTY_TLIST(_name, _list) (!(_list)->first)
+
+#endif
+