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#include <stdio.h>
#include <stdint.h>
#include <assert.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>
// TODO: do more error checking
#define BLOCK_SZ sizeof(struct_block)
#define BLOCK_ARR_CAP 1024
static inline void *_brk(void *addr) {
return (void *)syscall(SYS_brk, addr);
}
typedef uint64_t u64;
struct block {
void *addr; // pointer to the start address of the block
u64 size; // the size of the block
struct block *next; // pointer to the previous block
};
static void *heap_start;
static struct block *block_root;
static struct block block_arr[BLOCK_ARR_CAP];
void *mylloc(u64 size)
{
if(heap_start == NULL) {
heap_start = _brk(NULL);
}
void *addr = heap_start;
struct block *next = block_root;
struct block *prev = NULL;
// find the first available spot to allocate
while(next != NULL) {
if(size <= (u64)(next->addr - addr)) {
break;
}
addr += next->size;
prev = next;
next = next->next;
}
// no such spot, so extend the system break;
if(next == NULL) {
_brk(addr + size);
}
// find an empty block and fill it with information
for(int i = 0; i < BLOCK_ARR_CAP; i++) {
if(block_arr[i].addr != NULL) {
continue;
}
block_arr[i].addr = addr;
block_arr[i].size = size;
block_arr[i].next = next;
if(prev == NULL) {
block_root = &block_arr[i];
} else {
prev->next = &block_arr[i];
}
break;
}
return addr;
}
void myfree(void *addr)
{
struct block *prev = NULL;
struct block *block = block_root;
while(block != NULL)
{
if(block->addr != addr) {
prev = block;
block = block->next;
continue;
}
block->addr = NULL;
if(prev == NULL) {
block_root = block->next;
if(block->next == NULL) {
_brk(heap_start);
}
} else {
prev->next = block->next;
if(block->next == NULL) {
_brk(prev->addr + prev->size);
}
}
break;
}
}
int main(void)
{
char *str1 = mylloc(10);
memset(str1, '2', 10);
str1[9] = '\0';
char *str2 = mylloc(20);
memset(str2, '1', 20);
str2[19] = '\0';
myfree(str1);
char *str3 = mylloc(11);
memset(str3, '3', 11);
str3[10] = '\0';
printf("%s\n%s\n", str2, str3);
myfree(str3);
myfree(str2);
}
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