Sparse local attention

[Allianc-rgb]

Thanks for your greate job and paper, I learn a lot from it, But I have some questions:
I don’t quite understand the implementation of Sparse local Attention, The code in function sparse_local_attention_with_tensor_kernel :
for (int sz_idx = z_idx * z_stride - attend_range; sz_idx <= z_idx * z_stride + (z_stride - 1) + attend_range; ++sz_idx)
in which z_idx denotes z indices of non-empty voxels, What does sz_idx and z_stride mean? Look forward to your reply