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/************************************************************
* mm_free.c
*
* Copyright (C) 2007 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name Gregory Nutt nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
************************************************************/
/************************************************************
* Included Files
************************************************************/
#include <assert.h>
#include "mm_environment.h"
#include "mm_internal.h"
/************************************************************
* Definitions
************************************************************/
/************************************************************
* Private Functions
************************************************************/
/************************************************************
* Public Functions
************************************************************/
/************************************************************
* free
*
* Description:
* Returns a chunk of memory into the list of free nodes,
* merging with adjacent free chunks if possible.
*
************************************************************/
void free(FAR void *mem)
{
FAR struct mm_freenode_s *node;
FAR struct mm_freenode_s *prev;
FAR struct mm_freenode_s *next;
vdbg("Freeing %p\n", mem);
/* Protect against attempts to free a NULL reference */
if (!mem)
{
return;
}
/* We need to hold the MM semaphore while we muck with the
* nodelist.
*/
mm_takesemaphore();
/* Map the memory chunk into a free node */
node = (FAR struct mm_freenode_s *)((char*)mem - SIZEOF_MM_ALLOCNODE);
node->preceding &= ~MM_ALLOC_BIT;
/* Check if the following node is free and, if so, merge it */
next = (FAR struct mm_freenode_s *)((char*)node + node->size);
if ((next->preceding & MM_ALLOC_BIT) == 0)
{
FAR struct mm_allocnode_s *andbeyond;
/* Get the node following the next node (which will
* become the new next node). We know that we can never
* index past the tail chunk because it is always allocated.
*/
andbeyond = (FAR struct mm_allocnode_s*)((char*)next + next->size);
/* Remove the next node. There must be a predecessor,
* but there may not be a successor node.
*/
DEBUGASSERT(next->blink);
next->blink->flink = next->flink;
if (next->flink)
{
next->flink->blink = next->blink;
}
/* Then merge the two chunks */
node->size += next->size;
andbeyond->preceding = node->size | (andbeyond->preceding & MM_ALLOC_BIT);
next = (FAR struct mm_freenode_s *)andbeyond;
}
/* Check if the preceding node is also free and, if so, merge
* it with this node
*/
prev = (FAR struct mm_freenode_s *)((char*)node - node->preceding);
if ((prev->preceding & MM_ALLOC_BIT) == 0)
{
/* Remove the node. There must be a predecessor, but there may
* not be a successor node.
*/
DEBUGASSERT(prev->blink);
prev->blink->flink = prev->flink;
if (prev->flink)
{
prev->flink->blink = prev->blink;
}
/* Then merge the two chunks */
prev->size += node->size;
next->preceding = prev->size | (next->preceding & MM_ALLOC_BIT);
node = prev;
}
/* Add the merged node to the nodelist */
mm_addfreechunk(node);
mm_givesemaphore();
}
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