docstr: given the `val`, `a`, `wrap` which are the arguments in `fill_diagonal`,
  do some preprocess on `val` includes:
  
  1. calculate the length to fill on diagonal, 2-d and n-d(n > 2)
     as well as that `wrap` is True and `a` is a tall matrix need to be considered.
  2. if val is a Tensor, rechunk it into one chunk.
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code: def _process_val(val, a, wrap):
      """
      given the `val`, `a`, `wrap` which are the arguments in `fill_diagonal`,
      do some preprocess on `val` includes:
  
      1. calculate the length to fill on diagonal, 2-d and n-d(n > 2)
         as well as that `wrap` is True and `a` is a tall matrix need to be considered.
      2. if val is a Tensor, rechunk it into one chunk.
      """
  
      from ..datasource import diag
      from ..base import tile
  
      is_val_tensor = isinstance(val, TENSOR_TYPE)
  
      if a.ndim == 2:
          if wrap and TensorFillDiagonal._is_tall(a):
              size = sum(
                  diag(sub).shape[0]
                  for sub in TensorFillDiagonal._split_tall_matrix(a)
              )
          else:
              size = diag(a).shape[0]
      else:
          # every dimension has same shape
          size = a.shape[0]
  
      repeat_method = tile if is_val_tensor else np.tile
      val_size = val.size
      if val_size < size:
          n = ceildiv(size, val_size)
          val = repeat_method(val, n)[:size]
      elif val_size > size:
          val = val[:size]
  
      if is_val_tensor and val.ndim > 0:
          val = yield from recursive_tile(val)
          val = val.rechunk({0: val.size})
  
      return (yield from recursive_tile(val)) if is_val_tensor else val
  
imports: import numpy
  from ...None import opcodes
  from ...core import ENTITY_TYPE, recursive_tile
  from ...serialization.serializables import KeyField, AnyField, BoolField, Int32Field
  from ...utils import has_unknown_shape, ceildiv
  from ..operands import TensorOperand, TensorOperandMixin
  from ..datasource import tensor
  from ..array_utils import as_same_device, device
  from ..core import Tensor, TENSOR_TYPE
  from ..utils import decide_unify_split
label_desc: Use image node_id 8 for calling the TensorFillDiagonal obj's underlying member method code with example usage: obj._process_val(val, a, wrap) and returns: unknown