_malloc.c

void           *
_malloc(size_t size)
{
	void           *block_mem;
	block_t        *ptr, *newptr;
	size_t		alloc_size = size >= ALLOC_UNIT ? size + sizeof(block_t)
		: ALLOC_UNIT;
	ptr = head;
	while (ptr) {
		if (ptr->size >= size + sizeof(block_t)) {
			block_mem = BLOCK_MEM(ptr);
			fl_remove(ptr);
			if (ptr->size == size) {
				// we found a perfect sized block, return it
				return block_mem;
			}
			// our block is bigger then requested, split it and add
			// the spare to our free list
			newptr = split(ptr, size);
			fl_add(newptr);
			return block_mem;
		} else {
			ptr = ptr->next;
		}
	}
	/* We are unable to find a free block on our free list, so we
	 * should ask the OS for memory using sbrk. We will alloc
	 * more alloc_size bytes (probably way more than requested) and then
	 * split the newly allocated block to keep the spare space on our free
	 * list */
	ptr = sbrk(alloc_size);
	if (!ptr) {
		printf("failed to alloc %ld\n", alloc_size);
		return NULL;
	}
	ptr->next = NULL;
	ptr->prev = NULL;
	ptr->size = alloc_size - sizeof(block_t);
	if (alloc_size > size + sizeof(block_t)) {
		newptr = split(ptr, size);
		fl_add(newptr);
	}
	return BLOCK_MEM(ptr);
}