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import math |
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from typing import Optional |
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import torch |
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from torch import nn as nn, Tensor |
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from torch.nn import functional as F |
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from torch.nn.modules import transformer |
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from timm.models.vision_transformer import VisionTransformer, PatchEmbed |
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class DecoderLayer(nn.Module): |
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"""A Transformer decoder layer supporting two-stream attention (XLNet) |
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This implements a pre-LN decoder, as opposed to the post-LN default in PyTorch.""" |
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def __init__(self, d_model, nhead, dim_feedforward=2048, dropout=0.1, activation='gelu', |
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layer_norm_eps=1e-5): |
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super().__init__() |
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self.self_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout, batch_first=True) |
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self.cross_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout, batch_first=True) |
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self.linear1 = nn.Linear(d_model, dim_feedforward) |
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self.dropout = nn.Dropout(dropout) |
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self.linear2 = nn.Linear(dim_feedforward, d_model) |
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self.norm1 = nn.LayerNorm(d_model, eps=layer_norm_eps) |
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self.norm2 = nn.LayerNorm(d_model, eps=layer_norm_eps) |
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self.norm_q = nn.LayerNorm(d_model, eps=layer_norm_eps) |
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self.norm_c = nn.LayerNorm(d_model, eps=layer_norm_eps) |
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self.dropout1 = nn.Dropout(dropout) |
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self.dropout2 = nn.Dropout(dropout) |
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self.dropout3 = nn.Dropout(dropout) |
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self.activation = transformer._get_activation_fn(activation) |
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def __setstate__(self, state): |
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if 'activation' not in state: |
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state['activation'] = F.gelu |
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super().__setstate__(state) |
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def forward_stream(self, tgt: Tensor, tgt_norm: Tensor, tgt_kv: Tensor, memory: Tensor, tgt_mask: Optional[Tensor], |
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tgt_key_padding_mask: Optional[Tensor]): |
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"""Forward pass for a single stream (i.e. content or query) |
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tgt_norm is just a LayerNorm'd tgt. Added as a separate parameter for efficiency. |
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Both tgt_kv and memory are expected to be LayerNorm'd too. |
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memory is LayerNorm'd by ViT. |
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""" |
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tgt2, sa_weights = self.self_attn(tgt_norm, tgt_kv, tgt_kv, attn_mask=tgt_mask, |
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key_padding_mask=tgt_key_padding_mask) |
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tgt = tgt + self.dropout1(tgt2) |
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tgt2, ca_weights = self.cross_attn(self.norm1(tgt), memory, memory) |
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tgt = tgt + self.dropout2(tgt2) |
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tgt2 = self.linear2(self.dropout(self.activation(self.linear1(self.norm2(tgt))))) |
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tgt = tgt + self.dropout3(tgt2) |
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return tgt, sa_weights, ca_weights |
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def forward(self, query, content, memory, query_mask: Optional[Tensor] = None, content_mask: Optional[Tensor] = None, |
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content_key_padding_mask: Optional[Tensor] = None, update_content: bool = True): |
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query_norm = self.norm_q(query) |
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content_norm = self.norm_c(content) |
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query = self.forward_stream(query, query_norm, content_norm, memory, query_mask, content_key_padding_mask)[0] |
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if update_content: |
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content = self.forward_stream(content, content_norm, content_norm, memory, content_mask, |
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content_key_padding_mask)[0] |
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return query, content |
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class Decoder(nn.Module): |
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__constants__ = ['norm'] |
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def __init__(self, decoder_layer, num_layers, norm): |
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super().__init__() |
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self.layers = transformer._get_clones(decoder_layer, num_layers) |
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self.num_layers = num_layers |
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self.norm = norm |
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def forward(self, query, content, memory, query_mask: Optional[Tensor] = None, content_mask: Optional[Tensor] = None, |
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content_key_padding_mask: Optional[Tensor] = None): |
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for i, mod in enumerate(self.layers): |
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last = i == len(self.layers) - 1 |
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query, content = mod(query, content, memory, query_mask, content_mask, content_key_padding_mask, |
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update_content=not last) |
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query = self.norm(query) |
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return query |
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class Encoder(VisionTransformer): |
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def __init__(self, img_size=224, patch_size=16, in_chans=3, embed_dim=768, depth=12, num_heads=12, mlp_ratio=4., |
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qkv_bias=True, drop_rate=0., attn_drop_rate=0., drop_path_rate=0., embed_layer=PatchEmbed): |
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super().__init__(img_size, patch_size, in_chans, embed_dim=embed_dim, depth=depth, num_heads=num_heads, |
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mlp_ratio=mlp_ratio, qkv_bias=qkv_bias, drop_rate=drop_rate, attn_drop_rate=attn_drop_rate, |
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drop_path_rate=drop_path_rate, embed_layer=embed_layer, |
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num_classes=0, global_pool='', class_token=False) |
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def forward(self, x): |
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return self.forward_features(x) |
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class TokenEmbedding(nn.Module): |
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def __init__(self, charset_size: int, embed_dim: int): |
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super().__init__() |
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self.embedding = nn.Embedding(charset_size, embed_dim) |
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self.embed_dim = embed_dim |
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def forward(self, tokens: torch.Tensor): |
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return math.sqrt(self.embed_dim) * self.embedding(tokens) |
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