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+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+/**
+ * Intrusive linked lists.
+ *
+ * Singly-linked lists are declared like this:
+ *
+ * struct item {
+ * struct item *next;
+ * };
+ *
+ * struct list {
+ * struct item *head;
+ * struct item **tail;
+ * };
+ *
+ * The SLIST_*() macros manipulate singly-linked lists.
+ *
+ * struct list list;
+ * SLIST_INIT(&list);
+ *
+ * struct item item;
+ * SLIST_ITEM_INIT(&item);
+ * SLIST_APPEND(&list, &item);
+ *
+ * Doubly linked lists are similar:
+ *
+ * struct item {
+ * struct item *next;
+ * struct item *prev;
+ * };
+ *
+ * struct list {
+ * struct item *head;
+ * struct item *tail;
+ * };
+ *
+ * struct list list;
+ * LIST_INIT(&list);
+ *
+ * struct item item;
+ * LIST_ITEM_INIT(&item);
+ * LIST_APPEND(&list, &item);
+ *
+ * Items can be on multiple lists at once:
+ *
+ * struct item {
+ * struct {
+ * struct item *next;
+ * } chain;
+ *
+ * struct {
+ * struct item *next;
+ * struct item *prev;
+ * } lru;
+ * };
+ *
+ * struct items {
+ * struct {
+ * struct item *head;
+ * struct item **tail;
+ * } queue;
+ *
+ * struct {
+ * struct item *head;
+ * struct item *tail;
+ * } cache;
+ * };
+ *
+ * struct items items;
+ * SLIST_INIT(&items.queue);
+ * LIST_INIT(&items.cache);
+ *
+ * struct item item;
+ * SLIST_ITEM_INIT(&item, chain);
+ * SLIST_APPEND(&items.queue, &item, chain);
+ * LIST_ITEM_INIT(&item, lru);
+ * LIST_APPEND(&items.cache, &item, lru);
+ */
+
+#ifndef BFS_LIST_H
+#define BFS_LIST_H
+
+#include "diag.h"
+#include <stddef.h>
+#include <string.h>
+
+/**
+ * Initialize a singly-linked list.
+ *
+ * @param list
+ * The list to initialize.
+ *
+ * ---
+ *
+ * Like many macros in this file, this macro delegates the bulk of its work to
+ * some helper macros. We explicitly parenthesize (list) here so the helpers
+ * don't have to.
+ */
+#define SLIST_INIT(list) \
+ SLIST_INIT_((list))
+
+/**
+ * Helper for SLIST_INIT().
+ */
+#define SLIST_INIT_(list) LIST_VOID_( \
+ list->head = NULL, \
+ list->tail = &list->head)
+
+/**
+ * Cast a list of expressions to void.
+ */
+#define LIST_VOID_(...) ((void)(__VA_ARGS__))
+
+/**
+ * Initialize a singly-linked list item.
+ *
+ * @param item
+ * The item to initialize.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ *
+ * ---
+ *
+ * We play some tricks with variadic macros to handle the optional parameter:
+ *
+ * SLIST_ITEM_INIT(item) => item->next = NULL
+ * SLIST_ITEM_INIT(item, node) => item->node.next = NULL
+ *
+ * The first trick is that
+ *
+ * #define SLIST_ITEM_INIT(item, ...)
+ *
+ * won't work because both commas are required (until C23; see N3033). As a
+ * workaround, we dispatch to another macro and add a trailing comma.
+ *
+ * SLIST_ITEM_INIT(item) => SLIST_ITEM_INIT_(item, )
+ * SLIST_ITEM_INIT(item, node) => SLIST_ITEM_INIT_(item, node, )
+ */
+#define SLIST_ITEM_INIT(...) \
+ SLIST_ITEM_INIT_(__VA_ARGS__, )
+
+/**
+ * Now we need a way to generate either ->next or ->node.next depending on
+ * whether the node parameter was passed. The approach is based on
+ *
+ * #define FOO(...) BAR(__VA_ARGS__, 1, 2, )
+ * #define BAR(x, y, z, ...) z
+ *
+ * FOO(a) => 2
+ * FOO(a, b) => 1
+ *
+ * The LIST_NEXT_() macro uses this technique:
+ *
+ * LIST_NEXT_() => LIST_NODE_(next, )
+ * LIST_NEXT_(node, ) => LIST_NODE_(next, node, )
+ */
+#define LIST_NEXT_(...) \
+ LIST_NODE_(next, __VA_ARGS__)
+
+/**
+ * LIST_NODE_() dispatches to yet another macro:
+ *
+ * LIST_NODE_(next, ) => LIST_NODE__(next, , . , , )
+ * LIST_NODE_(next, node, ) => LIST_NODE__(next, node, , . , , )
+ */
+#define LIST_NODE_(dir, ...) \
+ LIST_NODE__(dir, __VA_ARGS__, . , , )
+
+/**
+ * And finally, LIST_NODE__() adds the node and the dot if necessary.
+ *
+ * dir node ignored dot
+ * v v v v
+ * LIST_NODE__(next, , . , , ) => next
+ * LIST_NODE__(next, node, , . , , ) => node . next
+ * ^ ^ ^ ^
+ * dir node ignored dot
+ */
+#define LIST_NODE__(dir, node, ignored, dot, ...) \
+ node dot dir
+
+/**
+ * SLIST_ITEM_INIT_() uses LIST_NEXT_() to generate the right name for the list
+ * node, and finally delegates to the actual implementation.
+ */
+#define SLIST_ITEM_INIT_(item, ...) \
+ SLIST_ITEM_INIT__((item), LIST_NEXT_(__VA_ARGS__))
+
+#define SLIST_ITEM_INIT__(item, next) \
+ LIST_VOID_(item->next = NULL)
+
+/**
+ * Type-checking macro for singly-linked lists.
+ */
+#define SLIST_CHECK_(list) \
+ (void)sizeof(list->tail - &list->head)
+
+/**
+ * Get the head of a singly-linked list.
+ *
+ * @param list
+ * The list in question.
+ * @return
+ * The first item in the list.
+ */
+#define SLIST_HEAD(list) \
+ SLIST_HEAD_((list))
+
+#define SLIST_HEAD_(list) \
+ (SLIST_CHECK_(list), list->head)
+
+/**
+ * Check if a singly-linked list is empty.
+ */
+#define SLIST_EMPTY(list) \
+ (!SLIST_HEAD(list))
+
+/**
+ * Like container_of(), but using the head pointer instead of offsetof() since
+ * we don't have the type around.
+ */
+#define SLIST_CONTAINER_(tail, head, next) \
+ (void *)((char *)tail - ((char *)&head->next - (char *)head))
+
+/**
+ * Get the tail of a singly-linked list.
+ *
+ * @param list
+ * The list in question.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ * @return
+ * The last item in the list.
+ */
+#define SLIST_TAIL(...) \
+ SLIST_TAIL_(__VA_ARGS__, )
+
+#define SLIST_TAIL_(list, ...) \
+ SLIST_TAIL__((list), LIST_NEXT_(__VA_ARGS__))
+
+#define SLIST_TAIL__(list, next) \
+ (list->head ? SLIST_CONTAINER_(list->tail, list->head, next) : NULL)
+
+/**
+ * Check if an item is attached to a singly-linked list.
+ *
+ * @param list
+ * The list to check.
+ * @param item
+ * The item to check.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ * @return
+ * Whether the item is attached to the list.
+ */
+#define SLIST_ATTACHED(list, ...) \
+ SLIST_ATTACHED_(list, __VA_ARGS__, )
+
+#define SLIST_ATTACHED_(list, item, ...) \
+ SLIST_ATTACHED__((list), (item), LIST_NEXT_(__VA_ARGS__))
+
+#define SLIST_ATTACHED__(list, item, next) \
+ (item->next || list->tail == &item->next)
+
+/**
+ * Insert an item into a singly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param cursor
+ * A pointer to the item to insert after, e.g. &list->head or list->tail.
+ * @param item
+ * The item to insert.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ * @return
+ * A cursor for the next item.
+ */
+#define SLIST_INSERT(list, cursor, ...) \
+ SLIST_INSERT_(list, cursor, __VA_ARGS__, )
+
+#define SLIST_INSERT_(list, cursor, item, ...) \
+ SLIST_INSERT__((list), (cursor), (item), LIST_NEXT_(__VA_ARGS__))
+
+#define SLIST_INSERT__(list, cursor, item, next) \
+ (bfs_assert(!SLIST_ATTACHED__(list, item, next)), \
+ item->next = *cursor, \
+ *cursor = item, \
+ list->tail = item->next ? list->tail : &item->next, \
+ &item->next)
+
+/**
+ * Add an item to the tail of a singly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param item
+ * The item to append.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ */
+#define SLIST_APPEND(list, ...) \
+ SLIST_APPEND_(list, __VA_ARGS__, )
+
+#define SLIST_APPEND_(list, item, ...) \
+ LIST_VOID_(SLIST_INSERT_(list, (list)->tail, item, __VA_ARGS__))
+
+/**
+ * Add an item to the head of a singly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param item
+ * The item to prepend.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ */
+#define SLIST_PREPEND(list, ...) \
+ SLIST_PREPEND_(list, __VA_ARGS__, )
+
+#define SLIST_PREPEND_(list, item, ...) \
+ LIST_VOID_(SLIST_INSERT_(list, &(list)->head, item, __VA_ARGS__))
+
+/**
+ * Add an entire singly-linked list to the tail of another.
+ *
+ * @param dest
+ * The destination list.
+ * @param src
+ * The source list.
+ */
+#define SLIST_EXTEND(dest, src) \
+ SLIST_EXTEND_((dest), (src))
+
+#define SLIST_EXTEND_(dest, src) \
+ (src->head ? (*dest->tail = src->head, dest->tail = src->tail, SLIST_INIT(src)) : (void)0)
+
+/**
+ * Remove an item from a singly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param cursor
+ * A pointer to the item to remove, either &list->head or &prev->next.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ * @return
+ * The removed item.
+ */
+#define SLIST_REMOVE(list, ...) \
+ SLIST_REMOVE_(list, __VA_ARGS__, )
+
+#define SLIST_REMOVE_(list, cursor, ...) \
+ SLIST_REMOVE__((list), (cursor), LIST_NEXT_(__VA_ARGS__))
+
+#define SLIST_REMOVE__(list, cursor, next) \
+ (list->tail = (*cursor)->next ? list->tail : cursor, \
+ slist_remove_impl(*cursor, cursor, &(*cursor)->next, sizeof(*cursor)))
+
+// Helper for SLIST_REMOVE()
+static inline void *slist_remove_impl(void *ret, void *cursor, void *next, size_t size) {
+ // ret = *cursor;
+ // *cursor = ret->next;
+ memcpy(cursor, next, size);
+ // ret->next = NULL;
+ memset(next, 0, size);
+ return ret;
+}
+
+/**
+ * Pop the head off a singly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param node (optional)
+ * If specified, use head->node.next rather than head->next.
+ * @return
+ * The popped item, or NULL if the list was empty.
+ */
+#define SLIST_POP(...) \
+ SLIST_POP_(__VA_ARGS__, )
+
+#define SLIST_POP_(list, ...) \
+ SLIST_POP__((list), __VA_ARGS__)
+
+#define SLIST_POP__(list, ...) \
+ (list->head ? SLIST_REMOVE_(list, &list->head, __VA_ARGS__) : NULL)
+
+/**
+ * Loop over the items in a singly-linked list.
+ *
+ * @param type
+ * The list item type.
+ * @param item
+ * The induction variable name.
+ * @param list
+ * The list to iterate.
+ * @param node (optional)
+ * If specified, use head->node.next rather than head->next.
+ */
+#define for_slist(type, item, ...) \
+ for_slist_(type, item, __VA_ARGS__, )
+
+#define for_slist_(type, item, list, ...) \
+ for_slist__(type, item, (list), LIST_NEXT_(__VA_ARGS__))
+
+#define for_slist__(type, item, list, next) \
+ for (type *item = list->head, *_next; \
+ item && (SLIST_CHECK_(list), _next = item->next, true); \
+ item = _next)
+
+/**
+ * Initialize a doubly-linked list.
+ *
+ * @param list
+ * The list to initialize.
+ */
+#define LIST_INIT(list) \
+ LIST_INIT_((list))
+
+#define LIST_INIT_(list) \
+ LIST_VOID_(list->head = list->tail = NULL)
+
+/**
+ * LIST_PREV_() => prev
+ * LIST_PREV_(node, ) => node.prev
+ */
+#define LIST_PREV_(...) \
+ LIST_NODE_(prev, __VA_ARGS__)
+
+/**
+ * Initialize a doubly-linked list item.
+ *
+ * @param item
+ * The item to initialize.
+ * @param node (optional)
+ * If specified, use item->node.next rather than item->next.
+ */
+#define LIST_ITEM_INIT(...) \
+ LIST_ITEM_INIT_(__VA_ARGS__, )
+
+#define LIST_ITEM_INIT_(item, ...) \
+ LIST_ITEM_INIT__((item), LIST_PREV_(__VA_ARGS__), LIST_NEXT_(__VA_ARGS__))
+
+#define LIST_ITEM_INIT__(item, prev, next) \
+ LIST_VOID_(item->prev = item->next = NULL)
+
+/**
+ * Type-checking macro for doubly-linked lists.
+ */
+#define LIST_CHECK_(list) \
+ (void)sizeof(list->tail - list->head)
+
+/**
+ * Check if a doubly-linked list is empty.
+ */
+#define LIST_EMPTY(list) \
+ LIST_EMPTY_((list))
+
+#define LIST_EMPTY_(list) \
+ (LIST_CHECK_(list), !list->head)
+
+/**
+ * Add an item to the tail of a doubly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param item
+ * The item to append.
+ * @param node (optional)
+ * If specified, use item->node.{prev,next} rather than item->{prev,next}.
+ */
+#define LIST_APPEND(list, ...) \
+ LIST_INSERT(list, (list)->tail, __VA_ARGS__)
+
+/**
+ * Add an item to the head of a doubly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param item
+ * The item to prepend.
+ * @param node (optional)
+ * If specified, use item->node.{prev,next} rather than item->{prev,next}.
+ */
+#define LIST_PREPEND(list, ...) \
+ LIST_INSERT(list, NULL, __VA_ARGS__)
+
+/**
+ * Check if an item is attached to a doubly-linked list.
+ *
+ * @param list
+ * The list to check.
+ * @param item
+ * The item to check.
+ * @param node (optional)
+ * If specified, use item->node.{prev,next} rather than item->{prev,next}.
+ * @return
+ * Whether the item is attached to the list.
+ */
+#define LIST_ATTACHED(list, ...) \
+ LIST_ATTACHED_(list, __VA_ARGS__, )
+
+#define LIST_ATTACHED_(list, item, ...) \
+ LIST_ATTACHED__((list), (item), LIST_PREV_(__VA_ARGS__), LIST_NEXT_(__VA_ARGS__))
+
+#define LIST_ATTACHED__(list, item, prev, next) \
+ (item->prev || item->next || list->head == item || list->tail == item)
+
+/**
+ * Insert into a doubly-linked list after the given cursor.
+ *
+ * @param list
+ * The list to modify.
+ * @param cursor
+ * Insert after this element.
+ * @param item
+ * The item to insert.
+ * @param node (optional)
+ * If specified, use item->node.{prev,next} rather than item->{prev,next}.
+ */
+#define LIST_INSERT(list, cursor, ...) \
+ LIST_INSERT_(list, cursor, __VA_ARGS__, )
+
+#define LIST_INSERT_(list, cursor, item, ...) \
+ LIST_INSERT__((list), (cursor), (item), LIST_PREV_(__VA_ARGS__), LIST_NEXT_(__VA_ARGS__))
+
+#define LIST_INSERT__(list, cursor, item, prev, next) LIST_VOID_( \
+ bfs_assert(!LIST_ATTACHED__(list, item, prev, next)), \
+ item->prev = cursor, \
+ item->next = cursor ? cursor->next : list->head, \
+ *(item->prev ? &item->prev->next : &list->head) = item, \
+ *(item->next ? &item->next->prev : &list->tail) = item)
+
+/**
+ * Remove an item from a doubly-linked list.
+ *
+ * @param list
+ * The list to modify.
+ * @param item
+ * The item to remove.
+ * @param node (optional)
+ * If specified, use item->node.{prev,next} rather than item->{prev,next}.
+ */
+#define LIST_REMOVE(list, ...) \
+ LIST_REMOVE_(list, __VA_ARGS__, )
+
+#define LIST_REMOVE_(list, item, ...) \
+ LIST_REMOVE__((list), (item), LIST_PREV_(__VA_ARGS__), LIST_NEXT_(__VA_ARGS__))
+
+#define LIST_REMOVE__(list, item, prev, next) LIST_VOID_( \
+ *(item->prev ? &item->prev->next : &list->head) = item->next, \
+ *(item->next ? &item->next->prev : &list->tail) = item->prev, \
+ item->prev = item->next = NULL)
+
+/**
+ * Loop over the items in a doubly-linked list.
+ *
+ * @param type
+ * The list item type.
+ * @param item
+ * The induction variable name.
+ * @param list
+ * The list to iterate.
+ * @param node (optional)
+ * If specified, use head->node.next rather than head->next.
+ */
+#define for_list(type, item, ...) \
+ for_list_(type, item, __VA_ARGS__, )
+
+#define for_list_(type, item, list, ...) \
+ for_list__(type, item, (list), LIST_NEXT_(__VA_ARGS__))
+
+#define for_list__(type, item, list, next) \
+ for (type *item = list->head, *_next; \
+ item && (LIST_CHECK_(list), _next = item->next, true); \
+ item = _next)
+
+#endif // BFS_LIST_H
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