/************************************************************
* mm_memalign.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
************************************************************/
/************************************************************
* Global Functions
************************************************************/
/************************************************************
* memalign
*
* Description:
* memalign requests more than enough space from malloc,
* finds a region within that chunk that meets the alignment
* request and then frees any leading or trailing space.
*
* The alignment argument must be a power of two (not
* checked). 8-byte alignment is guaranteed by normal
* malloc calls.
*
************************************************************/
FAR void *memalign(size_t alignment, size_t size)
{
FAR struct mm_allocnode_s *node;
size_t rawchunk;
size_t alignedchunk;
size_t mask = (size_t)(alignment - 1);
size_t allocsize;
/* If this requested alignement less than or equal to the
* natural alignment of malloc, then just let malloc do the
* work.
*/
if (alignment <= MM_MIN_CHUNK)
{
return malloc(size);
}
/* Adjust the size to account for (1) the size of the allocated
* node, (2) to make sure that it is an even multiple of
* our granule size, and to include the alignment amount.
*
* Notice that we increase the allocation size by twice the
* the requested alignment. We do this so that there will
* be at least two valid alignment points within the allocated
* memory.
*
* NOTE: These are sizes given to malloc and not chunk sizes.
* The do not include SIZEOF_MM_ALLOCNODE.
*/
size = MM_ALIGN_UP(size); /* Make mutliples of our granule size */
allocsize = size + 2*alignment; /* Add double full alignment size */
/* Then malloc that size */
rawchunk = (size_t)malloc(allocsize);
if (!rawchunk)
{
return NULL;
}
/* We need to hold the MM semaphore while we muck with the
* chunks and nodelist.
*/
mm_takesemaphore();
/* Get the node associated with the allocation and the next
* node after the allocation.
*/
node = (FAR struct mm_allocnode_s*)(rawchunk - SIZEOF_MM_ALLOCNODE);
/* Find the aligned subregion */
alignedchunk = (rawchunk + mask) & ~mask;
/* Check if there is free space at the beginning of the aligned chunk */
if (alignedchunk != rawchunk)
{
FAR struct mm_allocnode_s *newnode;
FAR struct mm_allocnode_s *next;
size_t precedingsize;
/* Get the node the next node after the allocation. */
next = (FAR struct mm_allocnode_s*)((char*)node + node->size);
/* Make sure that there is space to convert the preceding mm_allocnode_s
* into an mm_freenode_s. I think that this should always be true
*/
DEBUGASSERT(alignedchunk >= rawchunk + 8);
newnode = (FAR struct mm_allocnode_s*)(alignedchunk - SIZEOF_MM_ALLOCNODE);
/* Preceding size is full size of the new 'node,' including
* SIZEOF_MM_ALLOCNODE
*/
precedingsize = (size_t)newnode - (size_t)node;
/* If we were unlucky, then the alignedchunk can lie in such
* a position that precedingsize < SIZEOF_NODE_FREENODE. We
* can't let that happen because we are going to cast 'node' to
* struct mm_freenode_s below. This is why we allocated memory
* large enough to support two alignment points. In this case,
* we will simply use the second alignment point.
*/
if (precedingsize < SIZEOF_MM_FREENODE)
{
alignedchunk += alignment;
newnode = (FAR struct mm_allocnode_s*)(alignedchunk - SIZEOF_MM_ALLOCNODE);
precedingsize = (size_t)newnode - (size_t)node;
}
/* Set up the size of the new node */
newnode->size = (size_t)next - (size_t)newnode;
newnode->preceding = precedingsize | MM_ALLOC_BIT;
/* Reduce the size of the original chunk and mark it not allocated, */
node->size = precedingsize;
node->preceding &= ~MM_ALLOC_BIT;
/* Fix the preceding size of the next node */
next->preceding = newnode->size | (next->preceding & MM_ALLOC_BIT);
/* Convert the newnode chunk size back into malloc-compatible
* size by subtracting the header size SIZEOF_MM_ALLOCNODE.
*/
allocsize = newnode->size - SIZEOF_MM_ALLOCNODE;
/* Add the original, newly freed node to the free nodelist */
mm_addfreechunk((FAR struct mm_freenode_s *)node);
/* Replace the original node with the newlay realloaced,
* aligned node
*/
node = newnode;
}
/* Check if there is free space at the end of the aligned chunk */
if (allocsize > size)
{
/* Shrink the chunk by that much -- remember, mm_shrinkchunk
* wants internal chunk sizes that include SIZEOF_MM_ALLOCNODE,
* and not the malloc-compatible sizes that we have.
*/
mm_shrinkchunk(node, size + SIZEOF_MM_ALLOCNODE);
}
mm_givesemaphore();
return (FAR void*)alignedchunk;
}
