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import torch
import torch.nn as nn
import torch.nn.functional as F
from timm.models.layers import DropPath
class BiMultiHeadAttention(nn.Module):
def __init__(self, v_dim, l_dim, embed_dim, num_heads, dropout=0.1, cfg=None):
super(BiMultiHeadAttention, self).__init__()
self.embed_dim = embed_dim
self.num_heads = num_heads
self.head_dim = embed_dim // num_heads
self.v_dim = v_dim
self.l_dim = l_dim
assert (
self.head_dim * self.num_heads == self.embed_dim
), f"embed_dim must be divisible by num_heads (got `embed_dim`: {self.embed_dim} and `num_heads`: {self.num_heads})."
self.scale = self.head_dim ** (-0.5)
self.dropout = dropout
self.v_proj = nn.Linear(self.v_dim, self.embed_dim)
self.l_proj = nn.Linear(self.l_dim, self.embed_dim)
self.values_l_proj = nn.Linear(self.l_dim, self.embed_dim)
self.out_v_proj = nn.Linear(self.embed_dim, self.v_dim)
self.stable_softmax_2d = True
self.clamp_min_for_underflow = True
self.clamp_max_for_overflow = True
self._reset_parameters()
def _shape(self, tensor: torch.Tensor, seq_len: int, bsz: int):
return tensor.view(bsz, seq_len, self.num_heads, self.head_dim).transpose(1, 2).contiguous()
def _reset_parameters(self):
nn.init.xavier_uniform_(self.v_proj.weight)
self.v_proj.bias.data.fill_(0)
nn.init.xavier_uniform_(self.l_proj.weight)
self.l_proj.bias.data.fill_(0)
nn.init.xavier_uniform_(self.values_l_proj.weight)
self.values_l_proj.bias.data.fill_(0)
nn.init.xavier_uniform_(self.out_v_proj.weight)
self.out_v_proj.bias.data.fill_(0)
def forward(self, v, l, attention_mask_v=None, attention_mask_l=None):
bsz, tgt_len, _ = v.size()
query_states = self.v_proj(v) * self.scale
key_states = self._shape(self.l_proj(l), -1, bsz)
value_l_states = self._shape(self.values_l_proj(l), -1, bsz)
proj_shape = (bsz * self.num_heads, -1, self.head_dim)
query_states = self._shape(query_states, tgt_len, bsz).view(*proj_shape)
key_states = key_states.view(*proj_shape)
value_l_states = value_l_states.view(*proj_shape)
src_len = key_states.size(1)
attn_weights = torch.bmm(query_states, key_states.transpose(1, 2)) # bs*nhead, nimg, ntxt
if attn_weights.size() != (bsz * self.num_heads, tgt_len, src_len):
raise ValueError(
f"Attention weights should be of size {(bsz * self.num_heads, tgt_len, src_len)}, but is {attn_weights.size()}"
)
if self.stable_softmax_2d:
attn_weights = attn_weights - attn_weights.max()
if self.clamp_min_for_underflow:
attn_weights = torch.clamp(
attn_weights, min=-50000
) # Do not increase -50000, data type half has quite limited range
if self.clamp_max_for_overflow:
attn_weights = torch.clamp(
attn_weights, max=50000
) # Do not increase 50000, data type half has quite limited range
attn_weights_v = attn_weights.softmax(dim=-1)
attn_probs_v = F.dropout(attn_weights_v, p=self.dropout, training=self.training)
attn_output_v = torch.bmm(attn_probs_v, value_l_states)
if attn_output_v.size() != (bsz * self.num_heads, tgt_len, self.head_dim):
raise ValueError(
f"`attn_output_v` should be of size {(bsz, self.num_heads, tgt_len, self.head_dim)}, but is {attn_output_v.size()}"
)
attn_output_v = attn_output_v.view(bsz, self.num_heads, tgt_len, self.head_dim)
attn_output_v = attn_output_v.transpose(1, 2)
attn_output_v = attn_output_v.reshape(bsz, tgt_len, self.embed_dim)
attn_output_v = self.out_v_proj(attn_output_v)
return attn_output_v
# Bi-Direction MHA (text->image, image->text)
class BiAttentionBlock(nn.Module):
def __init__(
self,
v_dim,
l_dim,
embed_dim,
num_heads,
dropout=0.1,
drop_path=0.0,
cfg=None,
):
super(BiAttentionBlock, self).__init__()
# pre layer norm
self.layer_norm_v = nn.LayerNorm(v_dim)
self.layer_norm_l = nn.LayerNorm(l_dim)
self.attn = BiMultiHeadAttention(
v_dim=v_dim, l_dim=l_dim, embed_dim=embed_dim, num_heads=num_heads, dropout=dropout
)
# add layer scale for training stability
self.drop_path = DropPath(drop_path) if drop_path > 0.0 else nn.Identity()
def forward(self, v, l, attention_mask_v=None, attention_mask_l=None):
v = self.layer_norm_v(v)
l = self.layer_norm_l(l)
delta_v = self.attn(
v, l, attention_mask_v=attention_mask_v, attention_mask_l=attention_mask_l
)
delta_v = self.drop_path(delta_v)
return delta_v
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