private void shift(int target)
{
StackData s = stacks[(target + 1) % num_stack];
if (s.size >= s.capacity)
{
shift(target + 1);
}
for (int i = (s.start + s.capacity - 1) % (num_stack * default_size); s.isWithinStack(i, num_stack * default_size); i = last(i))
{
buffer[i] = buffer[last(i)];
}
buffer[s.start] = -1;
s.capacity--;
s.start = next(s.start);
s.pointer = next(s.pointer);
}