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 warnings
  import cupy
  from cupy._core import internal
  from cupy.linalg import lstsq
  import cupyx.scipy.fft
  from cupyx.scipy.ndimage import _util
  from cupyx.scipy.ndimage import _filters
  from cupyx.scipy.signal import _signaltools_core
  from cupyx.scipy.signal._arraytools import const_ext, even_ext, odd_ext, axis_reverse, axis_slice, axis_assign
  from cupyx.scipy.signal._iir_utils import apply_iir, apply_iir_sos, compute_correction_factors, compute_correction_factors_sos
label_desc: Use image node_id 20 for calling a global function with example usage: _validate_pad(padtype, padlen, x, axis, ntaps) and returns: edge,  ext