/*
* mm_free - Free a block by adding it to the appropriate list and coalescing
* it.
*/
void mm_free(void *ptr)
{
size_t size = GET_SIZE(HEAD(ptr)); /* Size of block */
/* Unset the reallocation tag on the next block */
UNSET_TAG(HEAD(NEXT(ptr)));
/* Adjust the allocation status in boundary tags */
PUT(HEAD(ptr), PACK(size, 0));
PUT(FOOT(ptr), PACK(size, 0));
/* Insert new block into appropriate list */
insert_node(ptr, size);
/* Coalesce free block */
coalesce(ptr);
/*
// Check heap for consistency
line_count++;
if (CHECK && CHECK_FREE) {
mm_check('f', ptr, size);
}
*/
return;
}
/*
* coalesce - Implements boundary-tag coalescing to merge the input block
* with any adjacent free blocks in constant time.
*/
static void *coalesce(void *bp) {
size_t prev_alloc = GET_PREV_ALLOC(HDRP(bp));
size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(bp)));
size_t size = GET_SIZE(HDRP(bp));
if (prev_alloc && next_alloc) { /* Case 1 */
UNSET_TAG(HDRP(NEXT_BLKP(bp)));
add_to_list(find_list(GET_SIZE(HDRP(bp))), bp);
return bp;
}
else if (prev_alloc && !next_alloc) { /* Case 2 */
remove_from_list(find_list(GET_SIZE(HDRP(NEXT_BLKP(bp)))), NEXT_BLKP(bp));
size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
PUT(HDRP(bp), PACK(size, 0));
PUT(FTRP(bp), PACK(size,0));
SET_TAG(HDRP(bp));
SET_TAG(FTRP(bp));
}
else if (!prev_alloc && next_alloc) { /* Case 3 */
remove_from_list(find_list(GET_SIZE(HDRP(PREV_BLKP(bp)))), PREV_BLKP(bp));
size += GET_SIZE(HDRP(PREV_BLKP(bp)));
SET_SIZE(FTRP(bp), size);
SET_SIZE(HDRP(PREV_BLKP(bp)), size);
bp = PREV_BLKP(bp);
}
else { /* Case 4 */
remove_from_list(find_list(GET_SIZE(HDRP(PREV_BLKP(bp)))), PREV_BLKP(bp));
remove_from_list(find_list(GET_SIZE(HDRP(NEXT_BLKP(bp)))), NEXT_BLKP(bp));
size += GET_SIZE(HDRP(PREV_BLKP(bp))) + GET_SIZE(FTRP(NEXT_BLKP(bp)));
SET_SIZE(HDRP(PREV_BLKP(bp)), size);
SET_SIZE(FTRP(NEXT_BLKP(bp)), size);
bp = PREV_BLKP(bp);
}
UNSET_TAG(HDRP(NEXT_BLKP(bp)));
add_to_list(find_list(GET_SIZE(HDRP(bp))), bp);
return bp;
}
