ar_next_buffer_index
return ar_next_buffer_index(ctx->last_buffer_index);
next_i = ar_next_buffer_index(i);
next_i = ar_next_buffer_index(next_i);
i = ar_next_buffer_index(i);
i = ar_next_buffer_index(i);
ar_next_buffer_index(i) * sizeof(struct descriptor));