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incubator-nuttx/mm/mm_realloc.c

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/************************************************************
* mm/mm_realloc.c
*
* Copyright (C) 2007, 2009 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 NuttX 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 <string.h>
#include "mm_environment.h"
#include <stdio.h> /* For NULL */
#include "mm_internal.h"
/************************************************************
* Pre-processor Definitions
************************************************************/
/************************************************************
* Global Functions
************************************************************/
/************************************************************
* realloc
*
* Description:
* If the reallocation is for less space, then:
* (1) the current allocation is reduced in size
* (2) the remainder at the end of the allocation is
* returned to the free list.
*
* If the request is for more space and the current
* allocation can be extended, it will be extended by:
* (1) Taking the additional space from the following
* free chunk, or
* (2) Taking the additional space from the preceding
* free chunk.
* (3) Or both
*
* If the request is for more space but the current chunk
* cannot be extended, then malloc a new buffer, copy the
* data into the new buffer, and free the old buffer.
*
************************************************************/
FAR void *realloc(FAR void *oldmem, size_t size)
{
FAR struct mm_allocnode_s *oldnode;
FAR struct mm_freenode_s *prev;
FAR struct mm_freenode_s *next;
size_t oldsize;
size_t prevsize = 0;
size_t nextsize = 0;
FAR void *newmem;
/* If oldmem is NULL, then realloc is equivalent to malloc */
if (!oldmem)
{
return malloc(size);
}
/* If size is zero, then realloc is equivalent to free */
if (size <= 0)
{
free(oldmem);
return NULL;
}
/* Adjust the size to account for (1) the size of the allocated
* node and (2) to make sure that it is an even multiple of
* our granule size.
*/
size = MM_ALIGN_UP(size + SIZEOF_MM_ALLOCNODE);
/* Map the memory chunk into an allocated node structure */
oldnode = (FAR struct mm_allocnode_s *)((FAR char*)oldmem - SIZEOF_MM_ALLOCNODE);
/* We need to hold the MM semaphore while we muck with the
* nodelist.
*/
mm_takesemaphore();
/* Check if this is a request to reduce the size of the allocation. */
oldsize = oldnode->size;
if (size <= oldsize)
{
/* Handle the special case where we are not going to change the
* size of the allocation.
*/
if (size < oldsize)
{
mm_shrinkchunk(oldnode, size);
}
/* Then return the original address */
mm_givesemaphore();
return oldmem;
}
/* This is a request to increase the size of the allocation, Get the
* available sizes before and after the oldnode so that we can make
* the best decision
*/
next = (FAR struct mm_freenode_s *)((FAR char*)oldnode + oldnode->size);
if ((next->preceding & MM_ALLOC_BIT) == 0)
{
nextsize = next->size;
}
prev = (FAR struct mm_freenode_s *)((FAR char*)oldnode - (oldnode->preceding & ~MM_ALLOC_BIT));
if ((prev->preceding & MM_ALLOC_BIT) == 0)
{
prevsize = prev->size;
}
/* Now, check if we can extend the current allocation or not */
if (nextsize + prevsize + oldsize >= size)
{
size_t needed = size - oldsize;
size_t takeprev = 0;
size_t takenext = 0;
/* Check if we can extend into the previous chunk and if the
* previous chunk is smaller than the next chunk.
*/
if (prevsize > 0 && (nextsize >= prevsize || nextsize <= 0))
{
/* Can we get everything we need from the previous chunk? */
if (needed > prevsize)
{
/* No, take the whole previous chunk and get the
* rest that we need from the next chunk.
*/
takeprev = prevsize;
takenext = needed - prevsize;
}
else
{
/* Yes, take what we need from the previous chunk */
takeprev = needed;
takenext = 0;
}
needed = 0;
}
/* Check if we can extend into the next chunk and if we still
* need more memory.
*/
if (nextsize > 0 && needed)
{
/* Can we get everything we need from the next chunk? */
if (needed > nextsize)
{
/* No, take the whole next chunk and get the
* rest that we need from the previous chunk.
*/
takeprev = needed - nextsize;
takenext = nextsize;
}
else
{
/* Yes, take what we need from the previous chunk */
takeprev = 0;
takenext = needed;
}
}
/* Extend into the previous free chunk */
newmem = oldmem;
if (takeprev)
{
FAR struct mm_allocnode_s *newnode;
/* Remove the previous 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;
}
/* Extend the node into the previous free chunk */
newnode = (FAR struct mm_allocnode_s *)((FAR char*)oldnode - takeprev);
/* Did we consume the entire preceding chunk? */
if (takeprev < prevsize)
{
/* No.. just take what we need from the previous chunk
* and put it back into the free list
*/
prev->size -= takeprev;
newnode->size = oldsize + takeprev;
newnode->preceding = prev->size | MM_ALLOC_BIT;
next->preceding = newnode->size | (next->preceding & MM_ALLOC_BIT);
/* Return the previous free node to the nodelist (with the new size) */
mm_addfreechunk(prev);
/* Now we want to return newnode */
oldnode = newnode;
}
else
{
/* Yes.. update its size (newnode->preceding is already set) */
newnode->size += oldsize;
newnode->preceding |= MM_ALLOC_BIT;
next->preceding = newnode->size | (next->preceding & MM_ALLOC_BIT);
}
oldnode = newnode;
oldsize = newnode->size;
/* Now we have to move the user contents 'down' in memory. memcpy should
* should be save for this.
*/
newmem = (FAR void*)((FAR char*)newnode + SIZEOF_MM_ALLOCNODE);
memcpy(newmem, oldmem, oldsize - SIZEOF_MM_ALLOCNODE);
}
/* Extend into the next free chunk */
if (takenext)
{
FAR struct mm_freenode_s *newnode;
FAR struct mm_allocnode_s *andbeyond;
/* Get the chunk following the next node (which could be the tail chunk) */
andbeyond = (FAR struct mm_allocnode_s*)((char*)next + nextsize);
/* 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;
}
/* Extend the node into the next chunk */
oldnode->size = oldsize + takenext;
newnode = (FAR struct mm_freenode_s *)((char*)oldnode + oldnode->size);
/* Did we consume the entire preceding chunk? */
if (takenext < nextsize)
{
/* No, take what we need from the next chunk and return it
* to the free nodelist.
*/
newnode->size = nextsize - takenext;
newnode->preceding = oldnode->size;
andbeyond->preceding = newnode->size | (andbeyond->preceding & MM_ALLOC_BIT);
/* Add the new free node to the nodelist (with the new size) */
mm_addfreechunk(newnode);
}
else
{
/* Yes, just update some pointers. */
andbeyond->preceding = oldnode->size | (andbeyond->preceding & MM_ALLOC_BIT);
}
}
mm_givesemaphore();
return newmem;
}
/* The current chunk cannot be extended. Just allocate a new chunk and copy */
else
{
/* Allocate a new block. On failure, realloc must return NULL but
* leave the original memory in place.
*/
mm_givesemaphore();
newmem = (FAR void*)malloc(size);
if (newmem)
{
memcpy(newmem, oldmem, oldsize);
free(oldmem);
}
return newmem;
}
}
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