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782e428284
This provides macros for managing intrusive doubly linked lists. There are many ways how to do those in a "generic" way in C. For example Solaris style lists are pretty nice: https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/common/sys/list.h https://github.com/illumos/illumos-gate/blob/master/usr/src/common/list/list.c I even have an independent implementation of this, which could be ISC licensed. But I think it's easier to vomit ~100 lines of preprocessor garbage, which has a lower footprint, and I think it wins slightly on the side of type safety, simplicity, and ease of use, even if it doesn't look as magically nice.
108 lines
5.0 KiB
C
108 lines
5.0 KiB
C
#pragma once
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#include <stddef.h>
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/*
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* Doubly linked list macros. All of these require that each list item is a
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* struct, that contains a field, that is another struct with prev/next fields:
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*
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* struct example_item {
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* struct {
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* struct example_item *prev, *next;
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* } mylist;
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* };
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*
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* And a struct somewhere that represents the "list" and has head/tail fields:
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*
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* struct {
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* struct example_item *head, *tail;
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* } mylist_var;
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*
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* Then you can e.g. insert elements like this:
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*
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* struct example_item item;
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* LL_APPEND(mylist, &mylist_var, &item);
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*
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* The first macro argument is always the name if the field in the item that
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* contains the prev/next pointers, in this case struct example_item.mylist.
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* This was done so that a single item can be in multiple lists.
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*
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* The list is started/terminated with NULL. Nothing ever points _to_ the
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* list head, so the list head memory location can be safely moved.
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*
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* General rules are:
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* - list head is initialized by setting head/tail to NULL
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* - list items do not need to be initialized before inserting them
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* - next/prev fields of list items are not cleared when they are removed
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* - there's no way to know whether an item is in the list or not (unless
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* you clear prev/next on init/removal, _and_ check whether items with
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* prev/next==NULL are referenced by head/tail)
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*/
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// Insert item at the end of the list (list->tail == item).
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// Undefined behavior if item is already in the list.
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#define LL_APPEND(field, list, item) do { \
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(item)->field.prev = (list)->tail; \
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(item)->field.next = NULL; \
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LL_RELINK_(field, list, item) \
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} while (0)
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// Insert item enew after eprev (i.e. eprev->next == enew). If eprev is NULL,
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// then insert it as head (list->head == enew).
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// Undefined behavior if enew is already in the list, or eprev isn't.
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#define LL_INSERT_AFTER(field, list, eprev, enew) do { \
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(enew)->field.prev = (eprev); \
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(enew)->field.next = (eprev) ? (eprev)->field.next : (list)->head; \
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LL_RELINK_(field, list, enew) \
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} while (0)
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// Insert item at the start of the list (list->head == item).
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// Undefined behavior if item is already in the list.
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#define LL_PREPEND(field, list, item) do { \
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(item)->field.prev = NULL; \
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(item)->field.next = (list)->head; \
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LL_RELINK_(field, list, item) \
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} while (0)
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// Insert item enew before enext (i.e. enew->next == enext). If enext is NULL,
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// then insert it as tail (list->tail == enew).
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// Undefined behavior if enew is already in the list, or enext isn't.
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#define LL_INSERT_BEFORE(field, list, enext, enew) do { \
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(enew)->field.prev = (enext) ? (enext)->field.prev : (list)->tail; \
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(enew)->field.next = (enext); \
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LL_RELINK_(field, list, enew) \
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} while (0)
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// Remove the item from the list.
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// Undefined behavior if item is not in the list.
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#define LL_REMOVE(field, list, item) do { \
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if ((item)->field.prev) { \
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(item)->field.prev->field.next = (item)->field.next; \
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} else { \
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(list)->head = (item)->field.next; \
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} \
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if ((item)->field.next) { \
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(item)->field.next->field.prev = (item)->field.prev; \
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} else { \
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(list)->tail = (item)->field.prev; \
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} \
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} while (0)
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// Remove all items from the list.
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#define LL_CLEAR(field, list) do { \
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(list)->head = (list)->tail = NULL; \
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} while (0)
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// Internal helper.
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#define LL_RELINK_(field, list, item) \
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if ((item)->field.prev) { \
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(item)->field.prev->field.next = (item); \
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} else { \
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(list)->head = (item); \
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} \
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if ((item)->field.next) { \
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(item)->field.next->field.prev = (item); \
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} else { \
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(list)->tail = (item); \
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}
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