#include <malloc.h>
#include <string.h>

/* See: https://8dcc.github.io/programming/pool-allocator.html */

#define CHUNK_SIZE 64

typedef union Chunk Chunk;
union Chunk {
    Chunk *next; // When not null, it is used
    char arr[CHUNK_SIZE];
};

typedef struct Pool Pool;
struct Pool {
    Chunk *free_chunk; // Pointer to a linked list of free chunks
    Chunk *chunk_arr;
};

void *pool_alloc(Pool *pool) {
    if (pool == NULL || pool->free_chunk == NULL)
        return NULL;

    // Pop a new one from the free list
    Chunk *result = pool->free_chunk;
    pool->free_chunk = pool->free_chunk->next;

    return result;
}

void pool_free(Pool *pool, void *ptr) {
    if (pool == NULL || ptr == NULL)
        return;

    // This can be done withuot an intermediate ptr
    Chunk *freed = ptr;
    freed->next = pool->free_chunk;
    pool->free_chunk = freed;
}

void pool_close(Pool *pool) {
    if (pool == NULL)
        return;

    free(pool->chunk_arr);
    free(pool);
}