content: import math
  import numpy as np
  
  import torch
  import torch.nn.functional as F
  from torch import nn
  from .weight_init import trunc_normal_
  
  
  class MaskedConv1D(nn.Module):
      """
      Masked 1D convolution. Interface remains the same as Conv1d.
      Only support a sub set of 1d convs
      """
      def __init__(
          self,
          in_channels,
          out_channels,
          kernel_size,
          stride=1,
          padding=0,
          dilation=1,
          groups=1,
          bias=True,
          padding_mode='zeros'
      ):
          super().__init__()
          # element must be aligned
          assert (kernel_size % 2 == 1) and (kernel_size // 2 == padding)
          # stride
          self.stride = stride
          self.conv = nn.Conv1d(in_channels, out_channels, kernel_size,
                                stride, padding, dilation, groups, bias, padding_mode)
          # zero out the bias term if it exists
          if bias:
              torch.nn.init.constant_(self.conv.bias, 0.)
  
      def forward(self, x, mask):
          # x: batch size, feature channel, sequence length,
          # mask: batch size, 1, sequence length (bool)
          B, C, T = x.size()
          # input length must be divisible by stride
          assert T % self.stride == 0
  
          # conv
          out_conv = self.conv(x)
          # compute the mask
          if self.stride > 1:
              # downsample the mask using nearest neighbor
              out_mask = F.interpolate(
                  mask.to(x.dtype),
                  size=T//self.stride,
                  mode='nearest'
              )
          else:
              # masking out the features
              out_mask = mask.to(x.dtype)
  
          # masking the output, stop grad to mask
          out_conv = out_conv * out_mask.detach()
          out_mask = out_mask.bool()
          return out_conv, out_mask
  
  
  class LayerNorm(nn.Module):
      """
      LayerNorm that supports inputs of size B, C, T
      """
      def __init__(
          self,
          num_channels,
          eps = 1e-5,
          affine = True,
          device = None,
          dtype = None,
      ):
          super().__init__()
          factory_kwargs = {'device': device, 'dtype': dtype}
          self.num_channels = num_channels
          self.eps = eps
          self.affine = affine
  
          if self.affine:
              self.weight = nn.Parameter(
                  torch.ones([1, num_channels, 1], **factory_kwargs))
              self.bias = nn.Parameter(
                  torch.zeros([1, num_channels, 1], **factory_kwargs))
          else:
              self.register_parameter('weight', None)
              self.register_parameter('bias', None)
  
      def forward(self, x):
          assert x.dim() == 3
          assert x.shape[1] == self.num_channels
  
          # normalization along C channels
          mu = torch.mean(x, dim=1, keepdim=True)
          res_x = x - mu
          sigma = torch.mean(res_x**2, dim=1, keepdim=True)
          out = res_x / torch.sqrt(sigma + self.eps)
  
          # apply weight and bias
          if self.affine:
              out *= self.weight
              out += self.bias
  
          return out
  
  
  # helper functions for Transformer blocks
  def get_sinusoid_encoding(n_position, d_hid):
      ''' Sinusoid position encoding table '''
  
      def get_position_angle_vec(position):
          return [position / np.power(10000, 2 * (hid_j // 2) / d_hid) for hid_j in range(d_hid)]
  
      sinusoid_table = np.array([get_position_angle_vec(pos_i) for pos_i in range(n_position)])
      sinusoid_table[:, 0::2] = np.sin(sinusoid_table[:, 0::2])  # dim 2i
      sinusoid_table[:, 1::2] = np.cos(sinusoid_table[:, 1::2])  # dim 2i+1
  
      # return a tensor of size 1 C T
      return torch.FloatTensor(sinusoid_table).unsqueeze(0).transpose(1, 2)
  
  
  # attention / transformers
  class MaskedMHA(nn.Module):
      """
      Multi Head Attention with mask
  
      Modified from https://github.com/karpathy/minGPT/blob/master/mingpt/model.py
      """
  
      def __init__(
          self,
          n_embd,          # dimension of the input embedding
          n_head,          # number of heads in multi-head self-attention
          attn_pdrop=0.0,  # dropout rate for the attention map
          proj_pdrop=0.0   # dropout rate for projection op
      ):
          super().__init__()
          assert n_embd % n_head == 0
          self.n_embd = n_embd
          self.n_head = n_head
          self.n_channels = n_embd // n_head
          self.scale = 1.0 / math.sqrt(self.n_channels)
  
          # key, query, value projections for all heads
          # it is OK to ignore masking, as the mask will be attached on the attention
          self.key = nn.Conv1d(self.n_embd, self.n_embd, 1)
          self.query = nn.Conv1d(self.n_embd, self.n_embd, 1)
          self.value = nn.Conv1d(self.n_embd, self.n_embd, 1)
  
          # regularization
          self.attn_drop = nn.Dropout(attn_pdrop)
          self.proj_drop = nn.Dropout(proj_pdrop)
  
          # output projection
          self.proj = nn.Conv1d(self.n_embd, self.n_embd, 1)
  
      def forward(self, x, mask):
          # x: batch size, feature channel, sequence length,
          # mask: batch size, 1, sequence length (bool)
          B, C, T = x.size()
  
          # calculate query, key, values for all heads in batch
          # (B, nh * hs, T)
          k = self.key(x)
          q = self.query(x)
          v = self.value(x)
  
          # move head forward to be the batch dim
          # (B, nh * hs, T) -> (B, nh, T, hs)
          k = k.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
          q = q.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
          v = v.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
  
          # self-attention: (B, nh, T, hs) x (B, nh, hs, T) -> (B, nh, T, T)
          att = (q * self.scale) @ k.transpose(-2, -1)
          # prevent q from attending to invalid tokens
          att = att.masked_fill(torch.logical_not(mask[:, :, None, :]), float('-inf'))
          # softmax attn
          att = F.softmax(att, dim=-1)
          att = self.attn_drop(att)
          # (B, nh, T, T) x (B, nh, T, hs) -> (B, nh, T, hs)
          out = att @ (v * mask[:, :, :, None].to(v.dtype))
          # re-assemble all head outputs side by side
          out = out.transpose(2, 3).contiguous().view(B, C, -1)
  
          # output projection + skip connection
          out = self.proj_drop(self.proj(out)) * mask.to(out.dtype)
          return out, mask
  
  
  class MaskedMHCA(nn.Module):
      """
      Multi Head Conv Attention with mask
  
      Add a depthwise convolution within a standard MHA
      The extra conv op can be used to
      (1) encode relative position information (relacing position encoding);
      (2) downsample the features if needed;
      (3) match the feature channels
  
      Note: With current implementation, the downsampled feature will be aligned
      to every s+1 time step, where s is the downsampling stride. This allows us
      to easily interpolate the corresponding positional embeddings.
  
      Modified from https://github.com/karpathy/minGPT/blob/master/mingpt/model.py
      """
  
      def __init__(
          self,
          n_embd,          # dimension of the output features
          n_head,          # number of heads in multi-head self-attention
          n_qx_stride=1,   # dowsampling stride for query and input
          n_kv_stride=1,   # downsampling stride for key and value
          attn_pdrop=0.0,  # dropout rate for the attention map
          proj_pdrop=0.0,  # dropout rate for projection op
      ):
          super().__init__()
          assert n_embd % n_head == 0
          self.n_embd = n_embd
          self.n_head = n_head
          self.n_channels = n_embd // n_head
          self.scale = 1.0 / math.sqrt(self.n_channels)
  
          # conv/pooling operations
          assert (n_qx_stride == 1) or (n_qx_stride % 2 == 0)
          assert (n_kv_stride == 1) or (n_kv_stride % 2 == 0)
          self.n_qx_stride = n_qx_stride
          self.n_kv_stride = n_kv_stride
  
          # query conv (depthwise)
          kernel_size = self.n_qx_stride + 1 if self.n_qx_stride > 1 else 3
          stride, padding = self.n_kv_stride, kernel_size // 2
          # 1d depthwise conv
          self.query_conv = MaskedConv1D(
              self.n_embd, self.n_embd, kernel_size,
              stride=stride, padding=padding, groups=self.n_embd, bias=False
          )
          # layernorm
          self.query_norm = LayerNorm(self.n_embd)
  
          # key, value conv (depthwise)
          kernel_size = self.n_kv_stride + 1 if self.n_kv_stride > 1 else 3
          stride, padding = self.n_kv_stride, kernel_size // 2
          # 1d depthwise conv
          self.key_conv = MaskedConv1D(
              self.n_embd, self.n_embd, kernel_size,
              stride=stride, padding=padding, groups=self.n_embd, bias=False
          )
          self.key_norm = LayerNorm(self.n_embd)
          self.value_conv = MaskedConv1D(
              self.n_embd, self.n_embd, kernel_size,
              stride=stride, padding=padding, groups=self.n_embd, bias=False
          )
          # layernorm
          self.value_norm = LayerNorm(self.n_embd)
  
          # key, query, value projections for all heads
          # it is OK to ignore masking, as the mask will be attached on the attention
          self.key = nn.Conv1d(self.n_embd, self.n_embd, 1)
          self.query = nn.Conv1d(self.n_embd, self.n_embd, 1)
          self.value = nn.Conv1d(self.n_embd, self.n_embd, 1)
  
          # regularization
          self.attn_drop = nn.Dropout(attn_pdrop)
          self.proj_drop = nn.Dropout(proj_pdrop)
  
          # output projection
          self.proj = nn.Conv1d(self.n_embd, self.n_embd, 1)
  
      def forward(self, x, mask):
          # x: batch size, feature channel, sequence length,
          # mask: batch size, 1, sequence length (bool)
          B, C, T = x.size()
  
          # query conv -> (B, nh * hs, T')
          q, qx_mask = self.query_conv(x, mask)
          q = self.query_norm(q)
          # key, value conv -> (B, nh * hs, T'')
          k, kv_mask = self.key_conv(x, mask)
          k = self.key_norm(k)
          v, _ = self.value_conv(x, mask)
          v = self.value_norm(v)
  
          # projections
          q = self.query(q)
          k = self.key(k)
          v = self.value(v)
  
          # move head forward to be the batch dim
          # (B, nh * hs, T'/T'') -> (B, nh, T'/T'', hs)
          k = k.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
          q = q.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
          v = v.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
  
          # self-attention: (B, nh, T', hs) x (B, nh, hs, T'') -> (B, nh, T', T'')
          att = (q * self.scale) @ k.transpose(-2, -1)
          # prevent q from attending to invalid tokens
          att = att.masked_fill(torch.logical_not(kv_mask[:, :, None, :]), float('-inf'))
          # softmax attn
          att = F.softmax(att, dim=-1)
          att = self.attn_drop(att)
          # (B, nh, T', T'') x (B, nh, T'', hs) -> (B, nh, T', hs)
          out = att @ (v * kv_mask[:, :, :, None].to(v.dtype))
          # re-assemble all head outputs side by side
          out = out.transpose(2, 3).contiguous().view(B, C, -1)
  
          # output projection + skip connection
          out = self.proj_drop(self.proj(out)) * qx_mask.to(out.dtype)
          return out, qx_mask
  
  
  class LocalMaskedMHCA(nn.Module):
      """
      Local Multi Head Conv Attention with mask
  
      Add a depthwise convolution within a standard MHA
      The extra conv op can be used to
      (1) encode relative position information (relacing position encoding);
      (2) downsample the features if needed;
      (3) match the feature channels
  
      Note: With current implementation, the downsampled feature will be aligned
      to every s+1 time step, where s is the downsampling stride. This allows us
      to easily interpolate the corresponding positional embeddings.
  
      The implementation is fairly tricky, code reference from
      https://github.com/huggingface/transformers/blob/master/src/transformers/models/longformer/modeling_longformer.py
      """
  
      def __init__(
          self,
          n_embd,          # dimension of the output features
          n_head,          # number of heads in multi-head self-attention
          window_size,     # size of the local attention window
          n_qx_stride=1,   # dowsampling stride for query and input
          n_kv_stride=1,   # downsampling stride for key and value
          attn_pdrop=0.0,  # dropout rate for the attention map
          proj_pdrop=0.0,  # dropout rate for projection op
          use_rel_pe=False # use relative position encoding
      ):
          super().__init__()
          assert n_embd % n_head == 0
          self.n_embd = n_embd
          self.n_head = n_head
          self.n_channels = n_embd // n_head
          self.scale = 1.0 / math.sqrt(self.n_channels)
          self.window_size = window_size
          self.window_overlap  = window_size // 2
          # must use an odd window size
          assert self.window_size > 1 and self.n_head >= 1
          self.use_rel_pe = use_rel_pe
  
          # conv/pooling operations
          assert (n_qx_stride == 1) or (n_qx_stride % 2 == 0)
          assert (n_kv_stride == 1) or (n_kv_stride % 2 == 0)
          self.n_qx_stride = n_qx_stride
          self.n_kv_stride = n_kv_stride
  
          # query conv (depthwise)
          kernel_size = self.n_qx_stride + 1 if self.n_qx_stride > 1 else 3
          stride, padding = self.n_kv_stride, kernel_size // 2
          # 1d depthwise conv
          self.query_conv = MaskedConv1D(
              self.n_embd, self.n_embd, kernel_size,
              stride=stride, padding=padding, groups=self.n_embd, bias=False
          )
          # layernorm
          self.query_norm = LayerNorm(self.n_embd)
  
          # key, value conv (depthwise)
          kernel_size = self.n_kv_stride + 1 if self.n_kv_stride > 1 else 3
          stride, padding = self.n_kv_stride, kernel_size // 2
          # 1d depthwise conv
          self.key_conv = MaskedConv1D(
              self.n_embd, self.n_embd, kernel_size,
              stride=stride, padding=padding, groups=self.n_embd, bias=False
          )
          self.key_norm = LayerNorm(self.n_embd)
          self.value_conv = MaskedConv1D(
              self.n_embd, self.n_embd, kernel_size,
              stride=stride, padding=padding, groups=self.n_embd, bias=False
          )
          # layernorm
          self.value_norm = LayerNorm(self.n_embd)
  
          # key, query, value projections for all heads
          # it is OK to ignore masking, as the mask will be attached on the attention
          self.key = nn.Conv1d(self.n_embd, self.n_embd, 1)
          self.query = nn.Conv1d(self.n_embd, self.n_embd, 1)
          self.value = nn.Conv1d(self.n_embd, self.n_embd, 1)
  
          # regularization
          self.attn_drop = nn.Dropout(attn_pdrop)
          self.proj_drop = nn.Dropout(proj_pdrop)
  
          # output projection
          self.proj = nn.Conv1d(self.n_embd, self.n_embd, 1)
  
          # relative position encoding
          if self.use_rel_pe:
              self.rel_pe = nn.Parameter(
                  torch.zeros(1, 1, self.n_head, self.window_size))
              trunc_normal_(self.rel_pe, std=(2.0 / self.n_embd)**0.5)
  
      @staticmethod
      def _chunk(x, window_overlap):
          """convert into overlapping chunks. Chunk size = 2w, overlap size = w"""
          # x: B x nh, T, hs
          # non-overlapping chunks of size = 2w -> B x nh, T//2w, 2w, hs
          x = x.view(
              x.size(0),
              x.size(1) // (window_overlap * 2),
              window_overlap * 2,
              x.size(2),
          )
  
          # use `as_strided` to make the chunks overlap with an overlap size = window_overlap
          chunk_size = list(x.size())
          chunk_size[1] = chunk_size[1] * 2 - 1
          chunk_stride = list(x.stride())
          chunk_stride[1] = chunk_stride[1] // 2
  
          # B x nh, #chunks = T//w - 1, 2w, hs
          return x.as_strided(size=chunk_size, stride=chunk_stride)
  
      @staticmethod
      def _pad_and_transpose_last_two_dims(x, padding):
          """pads rows and then flips rows and columns"""
          # padding value is not important because it will be overwritten
          x = nn.functional.pad(x, padding)
          x = x.view(*x.size()[:-2], x.size(-1), x.size(-2))
          return x
  
      @staticmethod
      def _mask_invalid_locations(input_tensor, affected_seq_len):
          beginning_mask_2d = input_tensor.new_ones(affected_seq_len, affected_seq_len + 1).tril().flip(dims=[0])
          beginning_mask = beginning_mask_2d[None, :, None, :]
          ending_mask = beginning_mask.flip(dims=(1, 3))
          beginning_input = input_tensor[:, :affected_seq_len, :, : affected_seq_len + 1]
          beginning_mask = beginning_mask.expand(beginning_input.size())
          # `== 1` converts to bool or uint8
          beginning_input.masked_fill_(beginning_mask == 1, -float("inf"))
          ending_input = input_tensor[:, -affected_seq_len:, :, -(affected_seq_len + 1) :]
          ending_mask = ending_mask.expand(ending_input.size())
          # `== 1` converts to bool or uint8
          ending_input.masked_fill_(ending_mask == 1, -float("inf"))
  
      @staticmethod
      def _pad_and_diagonalize(x):
          """
          shift every row 1 step right, converting columns into diagonals.
          Example::
                chunked_hidden_states: [ 0.4983,  2.6918, -0.0071,  1.0492,
                                         -1.8348,  0.7672,  0.2986,  0.0285,
                                         -0.7584,  0.4206, -0.0405,  0.1599,
                                         2.0514, -1.1600,  0.5372,  0.2629 ]
                window_overlap = num_rows = 4
               (pad & diagonalize) =>
               [ 0.4983,  2.6918, -0.0071,  1.0492, 0.0000,  0.0000,  0.0000
                 0.0000,  -1.8348,  0.7672,  0.2986,  0.0285, 0.0000,  0.0000
                 0.0000,  0.0000, -0.7584,  0.4206, -0.0405,  0.1599, 0.0000
                 0.0000,  0.0000,  0.0000, 2.0514, -1.1600,  0.5372,  0.2629 ]
          """
          total_num_heads, num_chunks, window_overlap, hidden_dim = x.size()
          # total_num_heads x num_chunks x window_overlap x (hidden_dim+window_overlap+1).
          x = nn.functional.pad(
              x, (0, window_overlap + 1)
          )
          # total_num_heads x num_chunks x window_overlap*window_overlap+window_overlap
          x = x.view(total_num_heads, num_chunks, -1)
          # total_num_heads x num_chunks x window_overlap*window_overlap
          x = x[:, :, :-window_overlap]
          x = x.view(
              total_num_heads, num_chunks, window_overlap, window_overlap + hidden_dim
          )
          x = x[:, :, :, :-1]
          return x
  
      def _sliding_chunks_query_key_matmul(
          self, query, key, num_heads, window_overlap
      ):
          """
          Matrix multiplication of query and key tensors using with a sliding window attention pattern. This implementation splits the input into overlapping chunks of size 2w with an overlap of size w (window_overlap)
          """
          # query / key: B*nh, T, hs
          bnh, seq_len, head_dim = query.size()
          batch_size = bnh // num_heads
          assert seq_len % (window_overlap * 2) == 0
          assert query.size() == key.size()
  
          chunks_count = seq_len // window_overlap - 1
  
          # B * num_heads, head_dim, #chunks=(T//w - 1), 2w
          chunk_query = self._chunk(query, window_overlap)
          chunk_key = self._chunk(key, window_overlap)
  
          # matrix multiplication
          # bcxd: batch_size * num_heads x chunks x 2window_overlap x head_dim
          # bcyd: batch_size * num_heads x chunks x 2window_overlap x head_dim
          # bcxy: batch_size * num_heads x chunks x 2window_overlap x 2window_overlap
          diagonal_chunked_attention_scores = torch.einsum(
              "bcxd,bcyd->bcxy", (chunk_query, chunk_key))
  
          # convert diagonals into columns
          # B * num_heads, #chunks, 2w, 2w+1
          diagonal_chunked_attention_scores = self._pad_and_transpose_last_two_dims(
              diagonal_chunked_attention_scores, padding=(0, 0, 0, 1)
          )
  
          # allocate space for the overall attention matrix where the chunks are combined. The last dimension
          # has (window_overlap * 2 + 1) columns. The first (window_overlap) columns are the window_overlap lower triangles (attention from a word to
          # window_overlap previous words). The following column is attention score from each word to itself, then
          # followed by window_overlap columns for the upper triangle.
          diagonal_attention_scores = diagonal_chunked_attention_scores.new_empty(
              (batch_size * num_heads, chunks_count + 1, window_overlap, window_overlap * 2 + 1)
          )
  
          # copy parts from diagonal_chunked_attention_scores into the combined matrix of attentions
          # - copying the main diagonal and the upper triangle
          diagonal_attention_scores[:, :-1, :, window_overlap:] = diagonal_chunked_attention_scores[
              :, :, :window_overlap, : window_overlap + 1
          ]
          diagonal_attention_scores[:, -1, :, window_overlap:] = diagonal_chunked_attention_scores[
              :, -1, window_overlap:, : window_overlap + 1
          ]
          # - copying the lower triangle
          diagonal_attention_scores[:, 1:, :, :window_overlap] = diagonal_chunked_attention_scores[
              :, :, -(window_overlap + 1) : -1, window_overlap + 1 :
          ]
  
          diagonal_attention_scores[:, 0, 1:window_overlap, 1:window_overlap] = diagonal_chunked_attention_scores[
              :, 0, : window_overlap - 1, 1 - window_overlap :
          ]
  
          # separate batch_size and num_heads dimensions again
          diagonal_attention_scores = diagonal_attention_scores.view(
              batch_size, num_heads, seq_len, 2 * window_overlap + 1
          ).transpose(2, 1)
  
          self._mask_invalid_locations(diagonal_attention_scores, window_overlap)
          return diagonal_attention_scores
  
      def _sliding_chunks_matmul_attn_probs_value(
          self, attn_probs, value, num_heads, window_overlap
      ):
          """
          Same as _sliding_chunks_query_key_matmul but for attn_probs and value tensors. Returned tensor will be of the
          same shape as `attn_probs`
          """
          bnh, seq_len, head_dim = value.size()
          batch_size = bnh // num_heads
          assert seq_len % (window_overlap * 2) == 0
          assert attn_probs.size(3) == 2 * window_overlap + 1
          chunks_count = seq_len // window_overlap - 1
          # group batch_size and num_heads dimensions into one, then chunk seq_len into chunks of size 2 window overlap
  
          chunked_attn_probs = attn_probs.transpose(1, 2).reshape(
              batch_size * num_heads, seq_len // window_overlap, window_overlap, 2 * window_overlap + 1
          )
  
          # pad seq_len with w at the beginning of the sequence and another window overlap at the end
          padded_value = nn.functional.pad(value, (0, 0, window_overlap, window_overlap), value=-1)
  
          # chunk padded_value into chunks of size 3 window overlap and an overlap of size window overlap
          chunked_value_size = (batch_size * num_heads, chunks_count + 1, 3 * window_overlap, head_dim)
          chunked_value_stride = padded_value.stride()
          chunked_value_stride = (
              chunked_value_stride[0],
              window_overlap * chunked_value_stride[1],
              chunked_value_stride[1],
              chunked_value_stride[2],
          )
          chunked_value = padded_value.as_strided(size=chunked_value_size, stride=chunked_value_stride)
  
          chunked_attn_probs = self._pad_and_diagonalize(chunked_attn_probs)
  
          context = torch.einsum("bcwd,bcdh->bcwh", (chunked_attn_probs, chunked_value))
          return context.view(batch_size, num_heads, seq_len, head_dim)
  
      def forward(self, x, mask):
          # x: batch size, feature channel, sequence length,
          # mask: batch size, 1, sequence length (bool)
          B, C, T = x.size()
  
          # step 1: depth convolutions
          # query conv -> (B, nh * hs, T')
          q, qx_mask = self.query_conv(x, mask)
          q = self.query_norm(q)
          # key, value conv -> (B, nh * hs, T'')
          k, kv_mask = self.key_conv(x, mask)
          k = self.key_norm(k)
          v, _ = self.value_conv(x, mask)
          v = self.value_norm(v)
  
          # step 2: query, key, value transforms & reshape
          # projections
          q = self.query(q)
          k = self.key(k)
          v = self.value(v)
          # (B, nh * hs, T) -> (B, nh, T, hs)
          q = q.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
          k = k.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
          v = v.view(B, self.n_head, self.n_channels, -1).transpose(2, 3)
          # view as (B * nh, T, hs)
          q = q.view(B * self.n_head, -1, self.n_channels).contiguous()
          k = k.view(B * self.n_head, -1, self.n_channels).contiguous()
          v = v.view(B * self.n_head, -1, self.n_channels).contiguous()
  
          # step 3: compute local self-attention with rel pe and masking
          q *= self.scale
          # chunked query key attention -> B, T, nh, 2w+1 = window_size
          att = self._sliding_chunks_query_key_matmul(
              q, k, self.n_head, self.window_overlap)
  
          # rel pe
          if self.use_rel_pe:
              att += self.rel_pe
          # kv_mask -> B, T'', 1
          inverse_kv_mask = torch.logical_not(
              kv_mask[:, :, :, None].view(B, -1, 1))
          # 0 for valid slot, -inf for masked ones
          float_inverse_kv_mask = inverse_kv_mask.type_as(q).masked_fill(
              inverse_kv_mask, -1e4)
          # compute the diagonal mask (for each local window)
          diagonal_mask = self._sliding_chunks_query_key_matmul(
              float_inverse_kv_mask.new_ones(size=float_inverse_kv_mask.size()),
              float_inverse_kv_mask,
              1,
              self.window_overlap
          )
          att += diagonal_mask
  
          # ignore input masking for now
          att = nn.functional.softmax(att, dim=-1)
          # softmax sometimes inserts NaN if all positions are masked, replace them with 0
          att = att.masked_fill(
              torch.logical_not(kv_mask.squeeze(1)[:, :, None, None]), 0.0)
          att = self.attn_drop(att)
  
          # step 4: compute attention value product + output projection
          # chunked attn value product -> B, nh, T, hs
          out = self._sliding_chunks_matmul_attn_probs_value(
              att, v, self.n_head, self.window_overlap)
          # transpose to B, nh, hs, T -> B, nh*hs, T
          out = out.transpose(2, 3).contiguous().view(B, C, -1)
          # output projection + skip connection
          out = self.proj_drop(self.proj(out)) * qx_mask.to(out.dtype)
          return out, qx_mask
  
  
  class TransformerBlock(nn.Module):
      """
      A simple (post layer norm) Transformer block
      Modified from https://github.com/karpathy/minGPT/blob/master/mingpt/model.py
      """
      def __init__(
          self,
          n_embd,                # dimension of the input features
          n_head,                # number of attention heads
          n_ds_strides=(1, 1),   # downsampling strides for q & x, k & v
          n_out=None,            # output dimension, if None, set to input dim
          n_hidden=None,         # dimension of the hidden layer in MLP
          act_layer=nn.GELU,     # nonlinear activation used in MLP, default GELU
          attn_pdrop=0.0,        # dropout rate for the attention map
          proj_pdrop=0.0,        # dropout rate for the projection / MLP
          path_pdrop=0.0,        # drop path rate
          mha_win_size=-1,       # > 0 to use window mha
          use_rel_pe=False       # if to add rel position encoding to attention
      ):
          super().__init__()
          assert len(n_ds_strides) == 2
          # layer norm for order (B C T)
          self.ln1 = LayerNorm(n_embd)
          self.ln2 = LayerNorm(n_embd)
  
          # specify the attention module
          if mha_win_size > 1:
              self.attn = LocalMaskedMHCA(
                  n_embd,
                  n_head,
                  window_size=mha_win_size,
                  n_qx_stride=n_ds_strides[0],
                  n_kv_stride=n_ds_strides[1],
                  attn_pdrop=attn_pdrop,
                  proj_pdrop=proj_pdrop,
                  use_rel_pe=use_rel_pe  # only valid for local attention
              )
          else:
              self.attn = MaskedMHCA(
                  n_embd,
                  n_head,
                  n_qx_stride=n_ds_strides[0],
                  n_kv_stride=n_ds_strides[1],
                  attn_pdrop=attn_pdrop,
                  proj_pdrop=proj_pdrop
              )
  
          # input
          if n_ds_strides[0] > 1:
              kernel_size, stride, padding = \
                  n_ds_strides[0] + 1, n_ds_strides[0], (n_ds_strides[0] + 1)//2
              self.pool_skip = nn.MaxPool1d(
                  kernel_size, stride=stride, padding=padding)
          else:
              self.pool_skip = nn.Identity()
  
          # two layer mlp
          if n_hidden is None:
              n_hidden = 4 * n_embd  # default
          if n_out is None:
              n_out = n_embd
          # ok to use conv1d here with stride=1
          self.mlp = nn.Sequential(
              nn.Conv1d(n_embd, n_hidden, 1),
              act_layer(),
              nn.Dropout(proj_pdrop, inplace=True),
              nn.Conv1d(n_hidden, n_out, 1),
              nn.Dropout(proj_pdrop, inplace=True),
          )
  
          # drop path
          if path_pdrop > 0.0:
              self.drop_path_attn = AffineDropPath(n_embd, drop_prob = path_pdrop)
              self.drop_path_mlp = AffineDropPath(n_out, drop_prob = path_pdrop)
          else:
              self.drop_path_attn = nn.Identity()
              self.drop_path_mlp = nn.Identity()
  
      def forward(self, x, mask, pos_embd=None):
          # pre-LN transformer: https://arxiv.org/pdf/2002.04745.pdf
          out, out_mask = self.attn(self.ln1(x), mask)
          out_mask_float = out_mask.to(out.dtype)
          out = self.pool_skip(x) * out_mask_float + self.drop_path_attn(out)
          # FFN
          out = out + self.drop_path_mlp(self.mlp(self.ln2(out)) * out_mask_float)
          # optionally add pos_embd to the output
          if pos_embd is not None:
              out += pos_embd * out_mask_float
          return out, out_mask
  
  
  class ConvBlock(nn.Module):
      """
      A simple conv block similar to the basic block used in ResNet
      """
      def __init__(
          self,
          n_embd,                # dimension of the input features
          kernel_size=3,         # conv kernel size
          n_ds_stride=1,         # downsampling stride for the current layer
          expansion_factor=2,    # expansion factor of feat dims
          n_out=None,            # output dimension, if None, set to input dim
          act_layer=nn.ReLU,     # nonlinear activation used after conv, default ReLU
      ):
          super().__init__()
          # must use odd sized kernel
          assert (kernel_size % 2 == 1) and (kernel_size > 1)
          padding = kernel_size // 2
          if n_out is None:
              n_out = n_embd
  
          # 1x3 (strided) -> 1x3 (basic block in resnet)
          width = n_embd * expansion_factor
          self.conv1 = MaskedConv1D(
              n_embd, width, kernel_size, n_ds_stride, padding=padding)
          self.conv2 = MaskedConv1D(
              width, n_out, kernel_size, 1, padding=padding)
  
          # attach downsampling conv op
          if n_ds_stride > 1:
              # 1x1 strided conv (same as resnet)
              self.downsample = MaskedConv1D(n_embd, n_out, 1, n_ds_stride)
          else:
              self.downsample = None
  
          self.act = act_layer()
  
      def forward(self, x, mask, pos_embd=None):
          identity = x
          out, out_mask = self.conv1(x, mask)
          out = self.act(out)
          out, out_mask = self.conv2(out, out_mask)
  
          # downsampling
          if self.downsample is not None:
              identity, _ = self.downsample(x, mask)
  
          # residual connection
          out += identity
          out = self.act(out)
  
          return out, out_mask
  
  
  # drop path: from https://github.com/facebookresearch/SlowFast/blob/master/slowfast/models/common.py
  class Scale(nn.Module):
      """
      Multiply the output regression range by a learnable constant value
      """
      def __init__(self, init_value=1.0):
          """
          init_value : initial value for the scalar
          """
          super().__init__()
          self.scale = nn.Parameter(
              torch.tensor(init_value, dtype=torch.float32),
              requires_grad=True
          )
  
      def forward(self, x):
          """
          input -> scale * input
          """
          return x * self.scale
  
  
  # The follow code is modified from
  # https://github.com/facebookresearch/SlowFast/blob/master/slowfast/models/common.py
  def drop_path(x, drop_prob=0.0, training=False):
      """
      Stochastic Depth per sample.
      """
      if drop_prob == 0.0 or not training:
          return x
      keep_prob = 1 - drop_prob
      shape = (x.shape[0],) + (1,) * (
          x.ndim - 1
      )  # work with diff dim tensors, not just 2D ConvNets
  