Simple question about llama adapter v1 transformer forward function

[Taehyung Noh]

Hello, first of all, thank you for the excellent work.

From my understanding of the paper, in Llama Adapter v1, the adaption prompt is inserted into the topmost L layers of the transformer.
However, in the code below, if self.adapter_layer is 30, doesn't it insert the adapter from the 3rd to the 32nd layer of the transformer?

Could you please explain why -1 * self.adapter_layer was used here?

https://github.com/OpenGVLab/LLaMA-Adapter/blob/8c50ee5d5d393c9bee5fcfda6aaea31d3ca3c40c/alpaca_finetuning_v1/llama/model.py

for layer in self.layers[: -1 * self.adapter_layer]:
                h = layer(h, start_pos, freqs_cis, mask)

for layer in self.layers[-1 * self.adapter_layer :]:
            h = layer(h, start_pos, freqs_cis, mask, adapter[adapter_index].half())
            adapter_index = adapter_index + 1

I really appreciate any help you can provide.