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38 * @(#)list.h 8.1 (Berkeley) 6/6/93
44 * Structures, macros, and routines exported by the List module.
55 * This module defines the list abstraction, which enables one to link
56 * together arbitrary data structures. Lists are doubly-linked and
57 * circular. A list contains a header followed by its real members, if
58 * any. (An empty list therefore consists of a single element, the
59 * header, whose nextPtr and prevPtr fields point to itself). To refer
60 * to a list as a whole, the user keeps a pointer to the header; that
61 * header is initialized by a call to List_Init(), which creates an empty
62 * list given a pointer to a List_Links structure (described below).
64 * The links are contained in a two-element structure called List_Links.
65 * A list joins List_Links records (that is, each List_Links structure
66 * points to other List_Links structures), but if the List_Links is the
67 * first field within a larger structure, then the larger structures are
68 * effectively linked together as follows:
71 * (List_Links) first elt. second elt.
72 * ----------------- ----------------- -----------------
73 * ..-> | nextPtr | ----> | List_Links | ----> | List_Links |----..
74 * | - - - - - - - | | | | |
75 * ..-- | prevPtr | <---- | | <---- | |<---..
76 * ----------------- - --- --- --- - - --- --- --- -
77 * | rest of | | rest of |
78 * | structure | | structure |
81 * ----------------- -----------------
83 * It is possible to link structures through List_Links fields that are
84 * not at the beginning of the larger structure, but it is then necessary
85 * to perform pointer arithmetic to find the beginning of the larger
86 * structure, given a pointer to some point within it.
88 * A typical structure might be something like:
96 * Before an element is inserted in a list for the first time, it must
97 * be initialized by calling the macro List_InitElement().
102 * data structure for lists
105 typedef struct List_Links {
106 struct List_Links *prevPtr;
107 struct List_Links *nextPtr;
114 void List_Init(); /* initialize a header to a list */
115 void List_Insert(); /* insert an element into a list */
116 void List_Remove(); /* remove an element from a list */
117 void List_Move(); /* move an element elsewhere in a list */
120 * ----------------------------------------------------------------------------
122 * List_InitElement --
124 * Initialize a list element. Must be called before an element is first
125 * inserted into a list.
127 * ----------------------------------------------------------------------------
129 #define List_InitElement(elementPtr) \
130 (elementPtr)->prevPtr = (List_Links *) NIL; \
131 (elementPtr)->nextPtr = (List_Links *) NIL;
134 * Macros for stepping through or selecting parts of lists
138 * ----------------------------------------------------------------------------
142 * Macro to loop through a list and perform an operation on each member.
144 * Usage: LIST_FORALL(headerPtr, itemPtr) {
146 * * operation on itemPtr, which points to successive members
149 * * It may be appropriate to first assign
150 * * foobarPtr = (Foobar *) itemPtr;
151 * * to refer to the entire Foobar structure.
155 * Note: itemPtr must be a List_Links pointer variable, and headerPtr
156 * must evaluate to a pointer to a List_Links structure.
158 * ----------------------------------------------------------------------------
161 #define LIST_FORALL(headerPtr, itemPtr) \
162 for (itemPtr = List_First(headerPtr); \
163 !List_IsAtEnd((headerPtr),itemPtr); \
164 itemPtr = List_Next(itemPtr))
167 * ----------------------------------------------------------------------------
171 * Macro: Boolean value, TRUE if the given list does not contain any
174 * Usage: if (List_IsEmpty(headerPtr)) ...
176 * ----------------------------------------------------------------------------
179 #define List_IsEmpty(headerPtr) \
180 ((headerPtr) == (headerPtr)->nextPtr)
183 * ----------------------------------------------------------------------------
187 * Macro: Boolean value, TRUE if itemPtr is after the end of headerPtr
188 * (i.e., itemPtr is the header of the list).
190 * Usage: if (List_IsAtEnd(headerPtr, itemPtr)) ...
192 * ----------------------------------------------------------------------------
196 #define List_IsAtEnd(headerPtr, itemPtr) \
197 ((itemPtr) == (headerPtr))
201 * ----------------------------------------------------------------------------
205 * Macro to return the first member in a list, which is the header if
208 * Usage: firstPtr = List_First(headerPtr);
210 * ----------------------------------------------------------------------------
213 #define List_First(headerPtr) ((headerPtr)->nextPtr)
216 * ----------------------------------------------------------------------------
220 * Macro to return the last member in a list, which is the header if
223 * Usage: lastPtr = List_Last(headerPtr);
225 * ----------------------------------------------------------------------------
228 #define List_Last(headerPtr) ((headerPtr)->prevPtr)
231 * ----------------------------------------------------------------------------
235 * Macro to return the member preceding the given member in its list.
236 * If the given list member is the first element in the list, List_Prev
237 * returns the list header.
239 * Usage: prevPtr = List_Prev(itemPtr);
241 * ----------------------------------------------------------------------------
244 #define List_Prev(itemPtr) ((itemPtr)->prevPtr)
247 * ----------------------------------------------------------------------------
251 * Macro to return the member following the given member in its list.
252 * If the given list member is the last element in the list, List_Next
253 * returns the list header.
255 * Usage: nextPtr = List_Next(itemPtr);
257 * ----------------------------------------------------------------------------
260 #define List_Next(itemPtr) ((itemPtr)->nextPtr)
264 * ----------------------------------------------------------------------------
265 * The List_Insert procedure takes two arguments. The first argument
266 * is a pointer to the structure to be inserted into a list, and
267 * the second argument is a pointer to the list member after which
268 * the new element is to be inserted. Macros are used to determine
269 * which existing member will precede the new one.
271 * The List_Move procedure takes a destination argument with the same
272 * semantics as List_Insert.
274 * The following macros define where to insert the new element
277 * LIST_AFTER(itemPtr) -- insert after itemPtr
278 * LIST_BEFORE(itemPtr) -- insert before itemPtr
279 * LIST_ATFRONT(headerPtr) -- insert at front of list
280 * LIST_ATREAR(headerPtr) -- insert at end of list
284 * List_Insert(itemPtr, LIST_AFTER(otherPtr));
286 * will insert itemPtr following otherPtr in the list containing otherPtr.
287 * ----------------------------------------------------------------------------
290 #define LIST_AFTER(itemPtr) ((List_Links *) itemPtr)
292 #define LIST_BEFORE(itemPtr) (((List_Links *) itemPtr)->prevPtr)
294 #define LIST_ATFRONT(headerPtr) ((List_Links *) headerPtr)
296 #define LIST_ATREAR(headerPtr) (((List_Links *) headerPtr)->prevPtr)