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babymalloc.c
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babymalloc.c
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#include "babymalloc.h"
#include <stdio.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <inttypes.h>
#define WSIZE sizeof(size_t)
#define FULL_BLOCK_MIN_SIZE ((2 * WSIZE) + WSIZE) // 2 words for header and footer, 1 word for payload
#define ALIGN(size) (((size) + (WSIZE - 1)) & ~(WSIZE - 1))
#define GET_SIZE(p) (*(size_t *) (p) & ~(WSIZE - 1))
#define GET_USED(p) (*(size_t *) (p) & 0x1) // 0 for free, 1 for used
#define SET_USED(p) (*(size_t *) (p) |= 0x1)
#define SET_FREE(p) (*(size_t *) (p) &= ~0x1)
#define GET_NEXT_BLKP(p) ((char *) (p) + GET_SIZE(p) + 2 * WSIZE)
#define GET_BLK_FOOTERP(p) ((char *) (p) + GET_SIZE(p) + WSIZE)
#define GET_PREV_BLKP(p) ((char *) (p) - (GET_SIZE((p) - WSIZE) + 2 * WSIZE))
#define GET_PAYLOAD(p) ((char *) (p) + WSIZE)
void *heap_startp;
void *heap_endp;
static void *extend_heap(size_t size);
static void *find_fit(size_t size);
static void insert_block(void *blkp, size_t size);
static void coalesce(void *blkp);
void *babymalloc(size_t size) {
size_t padding = -size & (WSIZE - 1);
size_t aligned_size = ALIGN(size);
// check for exceeding the maximum size or integer overflow
if (aligned_size > INTPTR_MAX - 2 * WSIZE || size > SIZE_MAX - padding) {
return NULL;
}
if (!heap_startp) {
heap_startp = extend_heap(aligned_size);
if (!heap_startp) {
return NULL;
}
heap_endp = GET_NEXT_BLKP(heap_startp);
}
void *blkp = find_fit(aligned_size);
if (blkp) {
insert_block(blkp, aligned_size);
return GET_PAYLOAD(blkp);
}
blkp = extend_heap(aligned_size);
if (!blkp) {
return NULL;
}
heap_endp = GET_NEXT_BLKP(blkp);
insert_block(blkp, aligned_size);
return GET_PAYLOAD(blkp);
}
void babyfree(void *ptr) {
void *blkp = (char *) ptr - WSIZE;
SET_FREE(blkp);
SET_FREE(GET_BLK_FOOTERP(blkp));
memset(ptr, 0, GET_SIZE(blkp));
coalesce(blkp);
}
void new_heap() {
size_t heap_size = (char *) heap_endp - (char *) heap_startp;
memset(heap_startp, 0, heap_size);
heap_startp = NULL;
heap_endp = NULL;
}
static void *extend_heap(size_t size) {
void *blkp = sbrk((intptr_t) size + 2 * WSIZE); // 2 words for header and footer
if (blkp == (void *) -1) {
return NULL;
}
*(size_t *) blkp = size;
*(size_t *) GET_BLK_FOOTERP(blkp) = size;
SET_FREE(blkp);
SET_FREE(GET_BLK_FOOTERP(blkp));
return blkp;
}
// first-fit algorithm
static void *find_fit(size_t size) {
void *blkp = heap_startp;
while (*(size_t *) blkp) {
if (!GET_USED(blkp) && *(size_t *) blkp >= size) {
return blkp;
}
blkp = GET_NEXT_BLKP(blkp);
}
return NULL;
}
static void insert_block(void *blkp, size_t size) {
if (GET_SIZE(blkp) - size >= FULL_BLOCK_MIN_SIZE) { // split the block if the remaining space is enough
size_t new_blk_size = GET_SIZE(blkp) - size - 2 * WSIZE;
*(size_t *) blkp = size;
*(size_t *) GET_BLK_FOOTERP(blkp) = size;
void *new_blkp = GET_NEXT_BLKP(blkp);
*(size_t *) new_blkp = new_blk_size;
*(size_t *) GET_BLK_FOOTERP(new_blkp) = new_blk_size;
SET_FREE(new_blkp);
SET_FREE(GET_BLK_FOOTERP(new_blkp));
}
SET_USED(blkp);
SET_USED(GET_BLK_FOOTERP(blkp));
}
static void coalesce(void *blkp) {
size_t blk_size = GET_SIZE(blkp);
void *prev_blkp = NULL;
void *next_blkp = GET_NEXT_BLKP(blkp);
int coalesce_prev = 0;
int coalesce_next = 0;
// check if the block is the first block
// if it is, we don't need to coalesce with the previous block
if (blkp == heap_startp) {
coalesce_prev = 0;
} else {
prev_blkp = GET_PREV_BLKP(blkp);
if (!GET_USED(prev_blkp)) {
coalesce_prev = 1;
}
}
// check if the block is the last block
// if it is, we don't need to coalesce with the next block
if (next_blkp >= heap_endp) {
coalesce_next = 0;
} else if (!GET_USED(next_blkp)) {
coalesce_next = 1;
}
if (coalesce_prev && coalesce_next) {
blk_size += GET_SIZE(prev_blkp) + GET_SIZE(next_blkp) + 4 * WSIZE;
*(size_t *) prev_blkp = blk_size;
*(size_t *) GET_BLK_FOOTERP(next_blkp) = blk_size;
SET_FREE(prev_blkp);
SET_FREE(GET_BLK_FOOTERP(next_blkp));
} else if (coalesce_prev) {
blk_size += GET_SIZE(prev_blkp) + 2 * WSIZE;
*(size_t *) prev_blkp = blk_size;
*(size_t *) GET_BLK_FOOTERP(blkp) = blk_size;
SET_FREE(prev_blkp);
SET_FREE(GET_BLK_FOOTERP(blkp));
} else if (coalesce_next) {
blk_size += GET_SIZE(next_blkp) + 2 * WSIZE;
*(size_t *) blkp = blk_size;
*(size_t *) GET_BLK_FOOTERP(next_blkp) = blk_size;
SET_FREE(blkp);
SET_FREE(GET_BLK_FOOTERP(next_blkp));
}
if (prev_blkp == heap_startp) {
*(size_t *) heap_startp = blk_size;
}
}
void print_heap() {
void *blkp = heap_startp;
while (*(size_t *) blkp) {
if (GET_USED(blkp)) {
printf("Block at %p: %zu size %zu, used\n", blkp, GET_SIZE(blkp), GET_SIZE(GET_BLK_FOOTERP(blkp)));
} else {
printf("Block at %p: %zu size %zu, free\n", blkp, GET_SIZE(blkp), GET_SIZE(GET_BLK_FOOTERP(blkp)));
}
blkp = GET_NEXT_BLKP(blkp);
}
}