struct FreeBlock {
	FreeBlock* next;
	size_t size;
};

(void*, size_t) allocate(size_t sz) {
	FreeBlock** prev = &root;
	FreeBlock* block = root;
	while (block) {
		if (block->size >= sz) {
			size_t tail = block->size - sz;
			if (tail >= sizeof(FreeBlock)) {
				FreeBlock* next = (FreeBlock*)((char*)block + sz);
				next->size = block->size - sz;
				next->next = block->next;
				block->next = next;
				block->size = sz;
			}
			*prev = block->next;
			return block, block->size;
		}
		prev = &block->next;
		block = *prev;
	}
}