code: def _validate_pad(padtype, padlen, x, axis, ntaps):
      """Helper to validate padding for filtfilt"""
      if padtype not in ["even", "odd", "constant", None]:
          raise ValueError(
              (
                  "Unknown value '%s' given to padtype.  padtype "
                  "must be 'even', 'odd', 'constant', or None."
              )
              % padtype
          )
  
      if padtype is None:
          padlen = 0
  
      if padlen is None:
          # Original padding; preserved for backwards compatibility.
          edge = ntaps * 3
      else:
          edge = padlen
  
      # x's 'axis' dimension must be bigger than edge.
      if x.shape[axis] <= edge:
          raise ValueError(
              "The length of the input vector x must be greater "
              "than padlen, which is %d." % edge
          )
  
      if padtype is not None and edge > 0:
          # Make an extension of length `edge` at each
          # end of the input array.
          if padtype == "even":
              ext = _even_ext(x, edge, axis=axis)
          elif padtype == "odd":
              ext = _odd_ext(x, edge, axis=axis)
          else:
              ext = _const_ext(x, edge, axis=axis)
      else:
          ext = x
      return edge, ext
  
imports: import cupy
  import numpy
  from cupyx.scipy import linalg
  from ..convolution.correlate import correlate
  from ..filter_design.filter_design_utils import _validate_sos
  from ..utils.arraytools import _axis_reverse, _axis_slice, _const_ext, _even_ext, _odd_ext
  from ..utils.helper_tools import _get_max_smem, _get_max_tpb
  from ._channelizer_cuda import _channelizer
  from ._sosfilt_cuda import _sosfilt
label_desc: Use image node_id 6 for calling a global function with example usage: _validate_pad(padtype, padlen, x, axis, ntaps) and returns: edge,  ext