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233 lines
6.3 KiB
233 lines
6.3 KiB
/*
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* Yet Another Malloc
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* ya_freelist.c
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*/
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/*----------*/
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/* Includes */
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/*----------*/
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#include <stdio.h>
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#include "ya_freelist.h"
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#include "ya_block.h"
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/*---------*/
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/* Globals */
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/*---------*/
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intptr_t *fl_start = NULL; // sorted increasing
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intptr_t *fl_end = NULL; // sorted decreasing
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/*-----------*/
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/* Functions */
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/*-----------*/
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/* Splices the allocated block out of the free list. */
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void fl_alloc(intptr_t *block) {
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intptr_t size = block_size(block);
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intptr_t *prev = fl_prev(block);
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intptr_t *next = fl_next(block);
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fl_set_prev(block, NULL);
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fl_set_next(block, NULL);
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if (prev) {
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fl_set_next(prev, next);
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} else {
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fl_start = next;
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}
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if (next) {
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fl_set_prev(next, prev);
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} else {
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fl_end = prev;
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}
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}
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/* Adds the freed block to the appropriate in the free list, which is kept
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* in sorted increasing order. */
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void fl_free(intptr_t *block) {
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if (!fl_start && !fl_end) {
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// add to empty list
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fl_set_prev(block, NULL);
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fl_set_next(block, NULL);
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fl_start = block;
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fl_end = block;
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return;
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}
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if (block < fl_start) {
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// preprend block to the free list
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fl_set_prev(block, NULL);
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fl_set_next(block, fl_start);
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fl_set_prev(fl_start, block);
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fl_start = block;
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return;
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}
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if (block > fl_end) {
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// append block to the free list
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fl_set_prev(block, fl_end);
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fl_set_next(block, NULL);
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fl_set_next(fl_end, block);
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fl_end = block;
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return;
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}
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// splice the block in the middle of the list
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intptr_t *next;
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for (next = fl_start; next && next < block; next = fl_next(next)) {
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// *whistle*
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}
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intptr_t *prev = fl_prev(next);
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fl_set_prev(block, prev);
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fl_set_next(block, next);
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fl_set_prev(next, block);
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fl_set_next(prev, block);
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}
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/* Returns the first block in the free list at min_size words long.
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* Returns NULL if no adequate block is found. Does not grow the heap. */
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intptr_t *fl_find(intptr_t min_size) {
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for (intptr_t *block = fl_start; block != NULL; block = fl_next(block)) {
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if (min_size <= block_size(block)) {
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return block;
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}
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}
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return NULL;
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}
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/* Mends the free list after a free block has just been split into two blocks,
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* block and new_next. */
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void fl_mend_split(intptr_t *block, intptr_t *new_next) {
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if (!new_next) {
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return; // block was not split
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}
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intptr_t *old_next = fl_next(new_next);
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fl_set_next(block, new_next);
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fl_set_prev(new_next, block);
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if (old_next) {
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fl_set_prev(old_next, new_next);
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} else {
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fl_end = new_next;
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}
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}
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void fl_join_next(intptr_t *block) {
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intptr_t *next = block + block_size(block);
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if (fl_next(block) == next) {
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// skip a block
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ya_debug("fl_join_next: %p:%ld + %p:%ld -> %p:%ld\n",
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block, block_size(block), next, block_size(next),
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block, block_size(block) + block_size(next));
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fl_set_next(block, fl_next(next));
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fl_set_prev(next, fl_prev(block));
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if (fl_next(next) == NULL) {
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fl_end = block;
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}
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}
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}
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void fl_join_prev(intptr_t *block) {
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intptr_t *free_prev = fl_prev(block);
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if (!free_prev) {
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return;
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}
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// will not segfault because there is at least one block preceding
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intptr_t *prev = block - block[-4];
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if (prev == free_prev) {
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ya_debug("fl_join_prev: %p:%ld + %p:%ld -> %p:%ld\n",
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block, block_size(block), prev, block_size(prev),
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prev, block_size(block) + block_size(prev));
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fl_set_prev(block, fl_prev(prev));
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fl_set_next(prev, fl_next(block));
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if (fl_next(block) == NULL) {
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fl_end = prev;
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}
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}
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}
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void fl_join(intptr_t *block) {
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fl_join_next(block);
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fl_join_prev(block);
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}
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/* Returns a pointer to the first free block. */
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intptr_t *fl_get_start() {
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return fl_start;
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}
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/* Returns a pointer to the last free block. */
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intptr_t *fl_get_end() {
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return fl_end;
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}
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#ifdef YA_DEBUG
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void fl_debug_print() {
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for (intptr_t *block = fl_start; block != NULL; block = fl_next(block)) {
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ya_debug("%p:%ld\n", block, block_size(block));
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}
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}
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/* Checks that block's information is consistent. The previous pointer should
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* point to correct_prev, which was the previous free block during free list
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* iteration.
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* Returns -1 on error, 0 otherwise. */
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int fl_check_one(intptr_t *block, intptr_t *correct_prev) {
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if (block < heap_start || block >= heap_end) {
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ya_debug("fl_check_one: block %p out of bounds\n", block);
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return -1;
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}
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intptr_t *prev = fl_prev(block);
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if (prev && (prev < heap_start || prev >= heap_end)) {
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ya_debug("fl_check_one: previous pointer %p out of bounds [%p,%p[\n",
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prev, heap_start, heap_end);
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return -1;
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}
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if (correct_prev != prev) {
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ya_debug("fl_check_one(%p): previous pointer mismatch, "
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"should be %p, not %p\n", block, correct_prev, prev);
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return -1;
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}
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intptr_t *next = fl_next(block);
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if (next && (next < heap_start || next >= heap_end)) {
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ya_debug("fl_check_one: next pointer %p out of bounds [%p,%p[\n",
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next, heap_start, heap_end);
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return -1;
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}
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return 0;
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}
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/* Checks the free list for consistency.
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* Returns -1 on error, the total number of free blocks otherwise. */
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int fl_check() {
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if (!fl_start) {
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if (fl_end) {
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ya_debug("fl_check: fl_start == NULL but fl_end == %p\n", fl_end);
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return -1;
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}
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return 0;
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}
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if (!fl_end) {
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ya_debug("fl_check: fl_end == NULL but fl_start == %p\n", fl_start);
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return -1;
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}
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if (fl_start < heap_start || fl_start >= heap_end) {
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ya_debug("fl_check: fl_start %p out of bounds\n", fl_start);
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return -1;
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}
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if (fl_end < heap_start || fl_end >= heap_end) {
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ya_debug("fl_check: fl_ebd %p out of bounds\n", fl_end);
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return -1;
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}
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int num_free = 0;
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intptr_t *prev = NULL;
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intptr_t *block;
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for (block = fl_start; block; block = fl_next(block)) {
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num_free++;
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if (fl_check_one(block, prev)) {
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return -1;
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}
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prev = block;
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}
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return num_free;
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}
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#endif // def YA_DEBUG
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