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- /*
- * libc/stdlib/malloc/heap_free.c -- return memory to a heap
- *
- * Copyright (C) 2002 NEC Corporation
- * Copyright (C) 2002 Miles Bader <miles@gnu.org>
- *
- * This file is subject to the terms and conditions of the GNU Lesser
- * General Public License. See the file COPYING.LIB in the main
- * directory of this archive for more details.
- *
- * Written by Miles Bader <miles@gnu.org>
- */
- #include <stdlib.h>
- #include "heap.h"
- /* Return the block of memory at MEM, of size SIZE, to HEAP. */
- struct heap_free_area *
- __heap_free (struct heap_free_area **heap, void *mem, size_t size)
- {
- struct heap_free_area *fa, *prev_fa;
- void *end = (char *)mem + size;
- HEAP_DEBUG (*heap, "before __heap_free");
- /* Find the right position in the free-list entry to place the new block.
- This is the most speed critical loop in this malloc implementation:
- since we use a simple linked-list for the free-list, and we keep it in
- address-sorted order, it can become very expensive to insert something
- in the free-list when it becomes fragmented and long. [A better
- implemention would use a balanced tree or something for the free-list,
- though that bloats the code-size and complexity quite a bit.] */
- for (prev_fa = 0, fa = *heap; fa; prev_fa = fa, fa = fa->next)
- if (unlikely (HEAP_FREE_AREA_END (fa) >= mem))
- break;
- if (fa && HEAP_FREE_AREA_START (fa) <= end)
- /* The free-area FA is adjacent to the new block, merge them. */
- {
- size_t fa_size = fa->size + size;
- if (HEAP_FREE_AREA_START (fa) == end)
- /* FA is just after the new block, grow down to encompass it. */
- {
- /* See if FA can now be merged with its predecessor. */
- if (prev_fa && mem == HEAP_FREE_AREA_END (prev_fa))
- /* Yup; merge PREV_FA's info into FA. */
- {
- fa_size += prev_fa->size;
- __heap_link_free_area_after (heap, fa, prev_fa->prev);
- }
- }
- else
- /* FA is just before the new block, expand to encompass it. */
- {
- struct heap_free_area *next_fa = fa->next;
- /* See if FA can now be merged with its successor. */
- if (next_fa && end == HEAP_FREE_AREA_START (next_fa))
- /* Yup; merge FA's info into NEXT_FA. */
- {
- fa_size += next_fa->size;
- __heap_link_free_area_after (heap, next_fa, prev_fa);
- fa = next_fa;
- }
- else
- /* FA can't be merged; move the descriptor for it to the tail-end
- of the memory block. */
- {
- /* The new descriptor is at the end of the extended block,
- SIZE bytes later than the old descriptor. */
- fa = (struct heap_free_area *)((char *)fa + size);
- /* Update links with the neighbors in the list. */
- __heap_link_free_area (heap, fa, prev_fa, next_fa);
- }
- }
- fa->size = fa_size;
- }
- else
- /* Make the new block into a separate free-list entry. */
- fa = __heap_add_free_area (heap, mem, size, prev_fa, fa);
- HEAP_DEBUG (*heap, "after __heap_free");
- return fa;
- }
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