/**************************************************************************** * mm/mm_realloc.c * * Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * 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 #include "mm_environment.h" #include #include "mm_internal.h" /**************************************************************************** * Pre-processor Definitions ****************************************************************************/ /**************************************************************************** * Global Functions ****************************************************************************/ /**************************************************************************** * Name: 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; } }