xref: /aosp_15_r20/external/mdnsresponder/mDNSShared/GenLinkedList.c (revision 48a54d368dc4fa860885eef7b70b6c53499e7c25)

/* -*- Mode: C; tab-width: 4 -*-
 *
 * Copyright (c) 2003 Apple Computer, Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.

 	File:		GenLinkedList.c

 	Contains:	implementation of generic linked lists.

 	Version:	1.0
 	Tabs:		4 spaces
 */

#include "GenLinkedList.h"


// Return the link pointer contained within element e at offset o.
#define		GETLINK( e, o)			( *(void**)((char*) (e) + (o)) )

// Assign the link pointer l to element e at offset o.
#define		ASSIGNLINK( e, l, o)	( *((void**)((char*) (e) + (o))) = (l))


//		GenLinkedList		/////////////////////////////////////////////////////////////

void		InitLinkedList( GenLinkedList *pList, size_t linkOffset)
/* Initialize the block of memory pointed to by pList as a linked list. */
{
	pList->Head = NULL;
	pList->Tail = NULL;
	pList->LinkOffset = linkOffset;
}


void		AddToTail( GenLinkedList *pList, void *elem)
/* Add a linked list element to the tail of the list. */
{
	if ( pList->Tail) {
		ASSIGNLINK( pList->Tail, elem, pList->LinkOffset);
	} else
		pList->Head = elem;
	ASSIGNLINK( elem, NULL, pList->LinkOffset);

	pList->Tail = elem;
}


void		AddToHead( GenLinkedList *pList, void *elem)
/* Add a linked list element to the head of the list. */
{
	ASSIGNLINK( elem, pList->Head, pList->LinkOffset);
	if ( pList->Tail == NULL)
		pList->Tail = elem;

	pList->Head = elem;
}


int		RemoveFromList( GenLinkedList *pList, void *elem)
/* Remove a linked list element from the list. Return 0 if it was not found. */
/* If the element is removed, its link will be set to NULL. */
{
void	*iElem, *lastElem;

	for ( iElem = pList->Head, lastElem = NULL; iElem; iElem = GETLINK( iElem, pList->LinkOffset)) {
		if ( iElem == elem) {
			if ( lastElem) {		// somewhere past the head
				ASSIGNLINK( lastElem, GETLINK( elem, pList->LinkOffset), pList->LinkOffset);
			} else {				// at the head
				pList->Head = GETLINK( elem, pList->LinkOffset);
			}
			if ( pList->Tail == elem)
				pList->Tail = lastElem ? lastElem : NULL;
			ASSIGNLINK( elem, NULL, pList->LinkOffset);			// maybe catch a stale reference bug.
			return 1;
		}
		lastElem = iElem;
	}

	return 0;
}


int			ReplaceElem( GenLinkedList *pList, void *elemInList, void *newElem)
/* Replace an element in the list with a new element, in the same position. */
{
void	*iElem, *lastElem;

	if ( elemInList == NULL || newElem == NULL)
		return 0;

	for ( iElem = pList->Head, lastElem = NULL; iElem; iElem = GETLINK( iElem, pList->LinkOffset))
	{
		if ( iElem == elemInList)
		{
			ASSIGNLINK( newElem, GETLINK( elemInList, pList->LinkOffset), pList->LinkOffset);
			if ( lastElem)		// somewhere past the head
			{
				ASSIGNLINK( lastElem, newElem, pList->LinkOffset);
			}
			else				// at the head
			{
				pList->Head = newElem;
			}
			if ( pList->Tail == elemInList)
				pList->Tail = newElem;
			return 1;
		}
		lastElem = iElem;
	}

	return 0;
}


//		GenDoubleLinkedList		/////////////////////////////////////////////////////////

void		InitDoubleLinkedList( GenDoubleLinkedList *pList, size_t fwdLinkOffset,
									  size_t backLinkOffset)
/* Initialize the block of memory pointed to by pList as a double linked list. */
{
	pList->Head = NULL;
	pList->Tail = NULL;
	pList->FwdLinkOffset = fwdLinkOffset;
	pList->BackLinkOffset = backLinkOffset;
}


void			DLLAddToHead( GenDoubleLinkedList *pList, void *elem)
/* Add a linked list element to the head of the list. */
{
void		*pNext;

	pNext = pList->Head;

	// fix up the forward links
	ASSIGNLINK( elem, pList->Head, pList->FwdLinkOffset);
	pList->Head = elem;

	// fix up the backward links
	if ( pNext) {
		ASSIGNLINK( pNext, elem, pList->BackLinkOffset);
	} else
		pList->Tail = elem;
	ASSIGNLINK( elem, NULL, pList->BackLinkOffset);
}


void			DLLRemoveFromList( GenDoubleLinkedList *pList, void *elem)
/* Remove a linked list element from the list. */
/* When the element is removed, its link will be set to NULL. */
{
void		*pNext, *pPrev;

	pNext = GETLINK( elem, pList->FwdLinkOffset);
	pPrev = GETLINK( elem, pList->BackLinkOffset);

	// fix up the forward links
	if ( pPrev)
		ASSIGNLINK( pPrev, pNext, pList->FwdLinkOffset);
	else
		pList->Head = pNext;

	// fix up the backward links
	if ( pNext)
		ASSIGNLINK( pNext, pPrev, pList->BackLinkOffset);
	else
		pList->Tail = pPrev;

	ASSIGNLINK( elem, NULL, pList->FwdLinkOffset);
	ASSIGNLINK( elem, NULL, pList->BackLinkOffset);
}


//		GenLinkedOffsetList		/////////////////////////////////////////////////////

// Extract the Next offset from element
#define		GETOFFSET( e, o)	( *(size_t*)((char*) (e) + (o)) )

static void		AssignOffsetLink( void *elem, void *link, size_t linkOffset);


static void	AssignOffsetLink( void *elem, void *link, size_t linkOffset)
// Assign link to elem as an offset from elem. Assign 0 to elem if link is NULL.
{
	GETOFFSET( elem, linkOffset) = link ? (size_t) link - (size_t) elem : 0;
}


void		*GetHeadPtr( GenLinkedOffsetList *pList)
/* Return a pointer to the head element of a list, or NULL if none. */
{
	return pList->Head ? ( (char*) (pList) + pList->Head) : NULL;
}


void		*GetTailPtr( GenLinkedOffsetList *pList)
/* Return a pointer to the tail element of a list, or NULL if none. */
{
	return pList->Tail ? ( (char*) (pList) + pList->Tail) : NULL;
}


void		*GetOffsetLink( GenLinkedOffsetList *pList, void *elem)
/* Return the link pointer contained within element e for pList, or NULL if it is 0. */
{
size_t		nextOffset;

	nextOffset = GETOFFSET( elem, pList->LinkOffset);

	return nextOffset ? (char*) elem + nextOffset : NULL;
}


void		InitLinkedOffsetList( GenLinkedOffsetList *pList, size_t linkOffset)
/* Initialize the block of memory pointed to by pList as a linked list. */
{
	pList->Head = 0;
	pList->Tail = 0;
	pList->LinkOffset = linkOffset;
}


void		OffsetAddToTail( GenLinkedOffsetList *pList, void *elem)
/* Add a linked list element to the tail of the list. */
{
	if ( pList->Tail) {
		AssignOffsetLink( GetTailPtr( pList), elem, pList->LinkOffset);
	} else
		pList->Head = (size_t) elem - (size_t) pList;
	AssignOffsetLink( elem, NULL, pList->LinkOffset);

	pList->Tail = (size_t) elem - (size_t) pList;
}


void		OffsetAddToHead( GenLinkedOffsetList *pList, void *elem)
/* Add a linked list element to the head of the list. */
{
	AssignOffsetLink( elem, GetHeadPtr( pList), pList->LinkOffset);
	if ( pList->Tail == 0)
		pList->Tail = (size_t) elem - (size_t) pList;

	pList->Head = (size_t) elem - (size_t) pList;
}


int		OffsetRemoveFromList( GenLinkedOffsetList *pList, void *elem)
/* Remove a linked list element from the list. Return 0 if it was not found. */
/* If the element is removed, its link will be set to NULL. */
{
void	*iElem, *lastElem;

	for ( iElem = GetHeadPtr( pList), lastElem = NULL; iElem;
		  iElem = GetOffsetLink( pList, iElem))
	{
		if ( iElem == elem) {
			if ( lastElem) {		// somewhere past the head
				AssignOffsetLink( lastElem, GetOffsetLink( pList, elem), pList->LinkOffset);
			} else {				// at the head
				iElem = GetOffsetLink( pList, elem);
				pList->Head = iElem ? (size_t) iElem - (size_t) pList : 0;
			}
			if ( GetTailPtr( pList) == elem)
				pList->Tail = lastElem ? (size_t) lastElem - (size_t) pList : 0;
			AssignOffsetLink( elem, NULL, pList->LinkOffset);	// maybe catch a stale reference bug.
			return 1;
		}
		lastElem = iElem;
	}

	return 0;
}


int			OffsetReplaceElem( GenLinkedOffsetList *pList, void *elemInList, void *newElem)
/* Replace an element in the list with a new element, in the same position. */
{
void	*iElem, *lastElem;

	if ( elemInList == NULL || newElem == NULL)
		return 0;

	for ( iElem = GetHeadPtr( pList), lastElem = NULL; iElem;
		  iElem = GetOffsetLink( pList, iElem))
	{
		if ( iElem == elemInList)
		{
			AssignOffsetLink( newElem, GetOffsetLink( pList, elemInList), pList->LinkOffset);
			if ( lastElem)		// somewhere past the head
			{
				AssignOffsetLink( lastElem, newElem, pList->LinkOffset);
			}
			else				// at the head
			{
				pList->Head = (size_t) newElem - (size_t) pList;
			}
			if ( GetTailPtr( pList) == elemInList)
				pList->Tail = (size_t) newElem - (size_t) pList;
			return 1;
		}
		lastElem = iElem;
	}

	return 0;
}