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107 lines (98 loc) · 5.01 KB
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#pragma once
#include <stddef.h>
/*
* Doubly linked list macros. All of these require that each list item is a
* struct, that contains a field, that is another struct with prev/next fields:
*
* struct example_item {
* struct {
* struct example_item *prev, *next;
* } mylist;
* };
*
* And a struct somewhere that represents the "list" and has head/tail fields:
*
* struct {
* struct example_item *head, *tail;
* } mylist_var;
*
* Then you can e.g. insert elements like this:
*
* struct example_item item;
* LL_APPEND(mylist, &mylist_var, &item);
*
* The first macro argument is always the name if the field in the item that
* contains the prev/next pointers, in this case struct example_item.mylist.
* This was done so that a single item can be in multiple lists.
*
* The list is started/terminated with NULL. Nothing ever points _to_ the
* list head, so the list head memory location can be safely moved.
*
* General rules are:
* - list head is initialized by setting head/tail to NULL
* - list items do not need to be initialized before inserting them
* - next/prev fields of list items are not cleared when they are removed
* - there's no way to know whether an item is in the list or not (unless
* you clear prev/next on init/removal, _and_ check whether items with
* prev/next==NULL are referenced by head/tail)
*/
// Insert item at the end of the list (list->tail == item).
// Undefined behavior if item is already in the list.
#define LL_APPEND(field, list, item) do { \
(item)->field.prev = (list)->tail; \
(item)->field.next = NULL; \
LL_RELINK_(field, list, item) \
} while (0)
// Insert item enew after eprev (i.e. eprev->next == enew). If eprev is NULL,
// then insert it as head (list->head == enew).
// Undefined behavior if enew is already in the list, or eprev isn't.
#define LL_INSERT_AFTER(field, list, eprev, enew) do { \
(enew)->field.prev = (eprev); \
(enew)->field.next = (eprev) ? (eprev)->field.next : (list)->head; \
LL_RELINK_(field, list, enew) \
} while (0)
// Insert item at the start of the list (list->head == item).
// Undefined behavior if item is already in the list.
#define LL_PREPEND(field, list, item) do { \
(item)->field.prev = NULL; \
(item)->field.next = (list)->head; \
LL_RELINK_(field, list, item) \
} while (0)
// Insert item enew before enext (i.e. enew->next == enext). If enext is NULL,
// then insert it as tail (list->tail == enew).
// Undefined behavior if enew is already in the list, or enext isn't.
#define LL_INSERT_BEFORE(field, list, enext, enew) do { \
(enew)->field.prev = (enext) ? (enext)->field.prev : (list)->tail; \
(enew)->field.next = (enext); \
LL_RELINK_(field, list, enew) \
} while (0)
// Remove the item from the list.
// Undefined behavior if item is not in the list.
#define LL_REMOVE(field, list, item) do { \
if ((item)->field.prev) { \
(item)->field.prev->field.next = (item)->field.next; \
} else { \
(list)->head = (item)->field.next; \
} \
if ((item)->field.next) { \
(item)->field.next->field.prev = (item)->field.prev; \
} else { \
(list)->tail = (item)->field.prev; \
} \
} while (0)
// Remove all items from the list.
#define LL_CLEAR(field, list) do { \
(list)->head = (list)->tail = NULL; \
} while (0)
// Internal helper.
#define LL_RELINK_(field, list, item) \
if ((item)->field.prev) { \
(item)->field.prev->field.next = (item); \
} else { \
(list)->head = (item); \
} \
if ((item)->field.next) { \
(item)->field.next->field.prev = (item); \
} else { \
(list)->tail = (item); \
}