code: def _get_shell_gap(filter_size):
      gap = 1
      while gap < filter_size:
          gap = 3 * gap + 1
      return gap
  
imports: import numpy
  import cupy
  from cupy import _core
  from cupy._core import internal
  from cupyx.scipy.ndimage import _util
  from cupyx.scipy.ndimage import _filters_core
  from cupyx.scipy.ndimage import _filters_generic
label_desc: Use image node_id 32 for calling a global function with example usage: _get_shell_gap(filter_size) and returns: gap