/*
* Place the block and potentially split the block
* Return: Nothing
*/
static void place(void *block, unsigned int awords) {
REQUIRES(awords >= 2 && awords % 2 == 0);
REQUIRES(block != NULL);
REQUIRES(in_heap(block));
REQUIRES(in_list(block));
unsigned int cwords = block_size(block); //the size of the given freeblock
block_delete(block); // delete block from the seg list
ENSURES(!in_list(block));
if ((cwords - awords) >= 4) {
set_size(block, awords);
block_mark(block, ALLOCATED);
block = block_next(block);
set_size(block, cwords - awords - 2);
block_mark(block, FREE);
block_insert(block);
ENSURES(in_list(block));
} else {
set_size(block, cwords);
block_mark(block, ALLOCATED);
}
}
/*
* Merge block with adjacent free blocks
* Return: the pointer to the new free block
*/
static void *coalesce(void *block) {
REQUIRES(block != NULL);
REQUIRES(in_heap(block));
uint32_t *prev_block = block_prev(block);
uint32_t *next_block = block_next(block);
int prev_free = block_free(prev_block);
int next_free = block_free(next_block);
unsigned int words = block_size(block);
if (prev_free && next_free) { // Case 4, both free
block_delete(prev_block);
block_delete(next_block);
words += block_size(prev_block) + block_size(next_block) + 4;
set_size(prev_block, words);
block_mark(prev_block, FREE);
block = (void *)prev_block;
block_insert(block);
ENSURES(in_list(block));
}
else if (!prev_free && next_free) { // Case 2, next if free
block_delete(next_block);
words += block_size(next_block) + 2;
set_size(block, words);
block_mark(block, FREE);
block_insert(block);
ENSURES(in_list(block));
}
else if (prev_free && !next_free) { // Case 3, prev is free
block_delete(prev_block);
words += block_size(prev_block) + 2;
set_size(prev_block, words);
block_mark(prev_block, FREE);
block = (void *)prev_block;
block_insert(block);
ENSURES(in_list(block));
}
else { // Case 1, both unfree
block_insert(block);
ENSURES(in_list(block));
return block;
}
return block;
}
// Returns a pointer if block of sufficient size is available
// will allocate a new block if none are free
static void* find_free_block(int index, size_t size){
REQUIRES(0 <= index && index < NUM_FREE_LISTS);
void* block;
void* current;
int new_index = index;
while(new_index < NUM_FREE_LISTS){
current = free_lists[new_index];
while(current != NULL){
if(block_size(current) >= size){
// if(new_index > index){
// block = split_block(new_index);
// block_mark(block, 0);
// return block;
// }
block = current;
block_mark(block, 0);
remove_block_from_list(new_index, block);
}
current = block_next(current);
}
new_index++;
}
assert(aligned(block));
block = allocate_block(size);
ENSURES(block != NULL);
return block;
}
/*
* free
*/
void free (void *ptr) {
if (ptr == NULL) {
return;
}
block_mark(get_header(ptr), 0);
coalesce(ptr);
}
/*
* Extends the heap with a new free block
* Return: the pointer to the new free block
* NULL on error.
*/
static void *extend_heap(unsigned int words) {
REQUIRES(words > 4);
uint32_t *block;
uint32_t *next;
/* Ask for 2 more words for header and footer */
words = (words % 2) ? (words + 1) : words;
if (VERBOSE)
printf("Extend Words = %d bytes\n", words * 4);
if ((long)(block = mem_sbrk(words * WSIZE)) == -1)
return NULL;
block--; // back step 1 since the last one is the epi block
set_size(block, words - 2);
block_mark(block, FREE);
ENSURES(block != NULL);
// New eqilogue block
next = block_next(block);
set_size(next, 0);
*next |= 0x40000000;
//block_mark(block_next(block), ALLOCATED);
ENSURES(!block_free(next));
ENSURES(block_size(next) == 0);
block = coalesce(block); // Coalesce if necessary
ENSURES(in_list(block));
return block;
}
/*
* free
*/
void free (void *ptr) {
/* If ptr is NULL, no operation is performed. */
if (ptr == NULL)
return;
uint32_t* block = block_block(ptr);
block_mark(block, FREE);
coalesce(block);
}
static void* allocate_block(size_t size){
void* block;
block = mem_sbrk(size);
if(block == NULL) return NULL;
set_size(block, size);
set_prev_pointer(block, NULL);
set_next_pointer(block, NULL);
block_mark(block, 0);
return block;
}
/*
* free
*/
void free (void *ptr) {
size_t size;
void* block;
int index;
checkheap(1);
if (ptr == NULL) {
return;
}
if(heap_start == 0)
mm_init();
block = block_from_ptr(ptr);
index = coalesce(block, &size);
block_mark(block, 1);
//set_prev_pointer(block, NULL);
//set_next_pointer(block, NULL);
add_block_to_list(index, block);
checkheap(1);
return;
}
/*
* Initialize: return -1 on error, 0 on success.
*/
int mm_init(void) {
/* Initialize the seg_list with NULL */
seg_list = mem_sbrk(SEG_LIST_SIZE * sizeof(uint32_t *));
for (int i = 0; i < SEG_LIST_SIZE; ++i) {
seg_list[i] = NULL;
}
if ((heap_listp = mem_sbrk(4 * WSIZE)) == (void *)-1)
return -1;
set_size(heap_listp, 0); // Allignment padding
set_size(heap_listp + 1, 0); // Pro of 0 size
set_size(heap_listp + 3, 0); // Epi of 0 size
(heap_listp + 3)[0] |= 0x40000000; // Mark epi as allocated
block_mark(heap_listp + 1, ALLOCATED); // Mark prologue as allocated
heap_listp += 1;
/* Extend the empty heap with a free block of CHUNKSIZE bytes
* extend_heap would ask for 2 more words */
if (extend_heap(CHUNKSIZE + 2) == NULL)
return -1;
return 0;
}
/*
* realloc - you may want to look at mm-naive.c
*/
void *realloc(void *oldptr, size_t size) {
if (oldptr == NULL) // if oldptr is NULL, this works as malloc(size)
return malloc(size);
if (size == 0) { // if size is 0, this works as free(oldptr)
free(oldptr);
return NULL;
}
uint32_t *block = block_block(oldptr);
REQUIRES(in_heap(block));
REQUIRES(!block_free(block));
unsigned int words = block_size(block); // old size in words
unsigned int nwords; // new size in words
uint32_t * ptr; // temp ptr
/* Adjust size to include alignment and convert to multipes of 4 bytes */
if (size <= DSIZE)
nwords = 2;
else
nwords = (((size) + (DSIZE-1)) & ~0x7) / WSIZE;
/* if new size is the same as old size or the old size is larger but no larger
* than 4 words, return oldptr without spliting */
//printf("RE, words = %d, nwords = %d\n", words, nwords);
if (nwords == words || (words > nwords && words - nwords < 4))
return oldptr;
else if (nwords < words) {
/* if old size is at least 4 words larger than new size
* return oldptr with spliting */
set_size(block, nwords);
block_mark(block, ALLOCATED);
ptr = block_next(block);
ENSURES(words - nwords - 2 < words);
set_size(ptr, words - nwords - 2);
block_mark(ptr, FREE);
block_insert(ptr);
return oldptr;
} else {
/* if old size is smaller than new size, look for more space */
ptr = block_next(block);
if (block_free(ptr)) {
ENSURES(in_list(ptr));
// if next block is free
unsigned int owords = block_size(ptr); //size of next blockdd
int remain = owords + 2 - (nwords - words);
if (remain >= 4) {
// the next free block is enough large to split
block_delete(ptr);
set_size(block, nwords);
block_mark(block, ALLOCATED);
ptr = block_next(block);
set_size(ptr, owords - (nwords - words));
block_mark(ptr, FREE);
block_insert(ptr);
return oldptr;
} else if (remain >= 0) {
// the next free block can not split
block_delete(ptr);
set_size(block, words + owords + 2);
block_mark(block, ALLOCATED);
return oldptr;
}
}
/* the next free block is too small, or
* next block is not free, malloc whole new one. */
ptr = malloc(size);
/* Copy the old data. */
memcpy(ptr, oldptr, block_size(block) * WSIZE);
/* Free the old block. */
free(oldptr);
return ptr;
}
}
