From 842f48c28b0b9b550391dfcafaabb4221684a7de Mon Sep 17 00:00:00 2001
From: Jon Santmyer <jon@jonsantmyer.com>
Date: Sat, 25 Jun 2022 12:28:33 -0400
Subject: Freestanding doubly linked list implementation

---
 llist.h | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 llist.h

diff --git a/llist.h b/llist.h
new file mode 100644
index 0000000..e5243bf
--- /dev/null
+++ b/llist.h
@@ -0,0 +1,103 @@
+/**
+ * llist.h
+ * Copyright (c) 2022 Jon Santmyer <jon@jonsantmyer.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+
+#ifndef LINKED_LIST_H
+#define LINKED_LIST_H 1
+
+#include <stddef.h>
+
+/*List member structs must begin with this struct as the first member*/
+struct llist_header
+{
+    struct llist_header *prev, *next;
+};
+
+/*Marks an unknown-state llist header as a single member circular list*/
+static inline void __llist_setup(struct llist_header *head)
+{
+    head->prev = head->next = head;
+}
+#define llist_setup(head) __llist_setup((struct llist_header*)(head))
+
+/*Fits a new node between prev and next*/
+static inline void __llist_add(struct llist_header *new, struct llist_header *prev, struct llist_header *next)
+{
+    new->prev = prev;
+    new->next = next;
+    prev->next = new;
+    next->prev = new;
+}
+
+#define llist_append(head, new) __llist_add(\
+        (struct llist_header*)(new), \
+        (struct llist_header*)(head), \
+        (struct llist_header*)(head->next))
+#define llist_prepend(head, new) __llist_add(\
+        (struct llist_header*)(new), \
+        (struct llist_header*)(head->prev), \
+        (struct llist_header*)(head))
+
+/*Seperates a node from prev and next, marking the removed as memberless*/
+static inline void __llist_del(struct llist_header *node, struct llist_header *prev, struct llist_header *next)
+{
+    prev->next = node->next;
+    next->prev = node->prev;
+    node->prev = node->next = NULL;
+}
+#define llist_del(node) __llist_del(\
+        (struct llist_header*)(node), \
+        (struct llist_header*)(node->prev), \
+        (struct llist_header*)(node->next))
+
+/*Returns the list header i elements ahead of head*/
+static inline struct llist_header *__llist_traverse(struct llist_header *head, size_t i)
+{
+    if(head == NULL) return NULL;
+    for(; i != 0 && head != NULL; head = head->next, i--);
+    return head;
+}
+#define llist_traverse(head, i) __list_traverse((struct llist_header*)(head), i)
+
+/*Returns how many jumps forwards it takes to reach find*/
+static inline int __llist_at(struct llist_header *head, struct llist_header *find)
+{
+    if(head == NULL) return -1;
+    int r = 1;
+    for(
+            struct llist_header *node = head->next; 
+            node != head; 
+            node = node->next, r++) {
+        if(node == find) return ++r;
+    }
+    return -1;
+}
+#define llist_at(head, find) __llist_at(\
+        (struct llist_header*)(head), \
+        (struct llist_header*)(find))
+
+/*Define for easily looping through a llist*/
+#define llist_foreach(node, head) \
+    for(struct llist_header *node = head->next; node != head; node = node->next)
+
+#endif
-- 
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