Why the value n in dataset.py function get_seg_range is subtracted 1 twice?

[TyroneLi]

Hi~I am confused about this operation as I mention in title.Inside dataset.py function get_seg_range, n is subtracted 1 twice.could u make some more expression details?Thanks
``def get_seg_range(n, num_segments, seg, representation):
if representation in ['residual', 'mv']:
n -= 1
seg_size = float(n - 1) / num_segments
seg_begin = int(np.round(seg_size * seg))
seg_end = int(np.round(seg_size * (seg+1)))
if seg_end == seg_begin:
seg_end = seg_begin + 1

if representation in ['residual', 'mv']:
    # Exclude the 0-th frame, because it's an I-frmae.
    return seg_begin + 1, seg_end + 1

return seg_begin, seg_end``