import os
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import math
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import torch
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import torch.nn as nn
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class OnnxMultiHeadedAttention(nn.Module):
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def __init__(self, model):
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super().__init__()
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self.d_k = model.d_k
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self.h = model.h
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self.linear_q = model.linear_q
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self.linear_k = model.linear_k
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self.linear_v = model.linear_v
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self.linear_out = model.linear_out
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self.attn = None
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self.all_head_size = self.h * self.d_k
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def forward(self, query, key, value, mask):
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q, k, v = self.forward_qkv(query, key, value)
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scores = torch.matmul(q, k.transpose(-2, -1)) / math.sqrt(self.d_k)
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return self.forward_attention(v, scores, mask)
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def transpose_for_scores(self, x: torch.Tensor) -> torch.Tensor:
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new_x_shape = x.size()[:-1] + (self.h, self.d_k)
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x = x.view(new_x_shape)
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return x.permute(0, 2, 1, 3)
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def forward_qkv(self, query, key, value):
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q = self.linear_q(query)
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k = self.linear_k(key)
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v = self.linear_v(value)
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q = self.transpose_for_scores(q)
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k = self.transpose_for_scores(k)
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v = self.transpose_for_scores(v)
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return q, k, v
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def forward_attention(self, value, scores, mask):
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scores = scores + mask
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self.attn = torch.softmax(scores, dim=-1)
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context_layer = torch.matmul(self.attn, value) # (batch, head, time1, d_k)
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context_layer = context_layer.permute(0, 2, 1, 3).contiguous()
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new_context_layer_shape = context_layer.size()[:-2] + (self.all_head_size,)
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context_layer = context_layer.view(new_context_layer_shape)
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return self.linear_out(context_layer) # (batch, time1, d_model)
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class OnnxRelPosMultiHeadedAttention(OnnxMultiHeadedAttention):
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def __init__(self, model):
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super().__init__(model)
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self.linear_pos = model.linear_pos
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self.pos_bias_u = model.pos_bias_u
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self.pos_bias_v = model.pos_bias_v
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def forward(self, query, key, value, pos_emb, mask):
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q, k, v = self.forward_qkv(query, key, value)
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q = q.transpose(1, 2) # (batch, time1, head, d_k)
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p = self.transpose_for_scores(self.linear_pos(pos_emb)) # (batch, head, time1, d_k)
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# (batch, head, time1, d_k)
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q_with_bias_u = (q + self.pos_bias_u).transpose(1, 2)
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# (batch, head, time1, d_k)
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q_with_bias_v = (q + self.pos_bias_v).transpose(1, 2)
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# compute attention score
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# first compute matrix a and matrix c
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# as described in https://arxiv.org/abs/1901.02860 Section 3.3
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# (batch, head, time1, time2)
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matrix_ac = torch.matmul(q_with_bias_u, k.transpose(-2, -1))
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# compute matrix b and matrix d
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# (batch, head, time1, time1)
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matrix_bd = torch.matmul(q_with_bias_v, p.transpose(-2, -1))
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matrix_bd = self.rel_shift(matrix_bd)
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scores = (matrix_ac + matrix_bd) / math.sqrt(
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self.d_k
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) # (batch, head, time1, time2)
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return self.forward_attention(v, scores, mask)
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def rel_shift(self, x):
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zero_pad = torch.zeros((*x.size()[:3], 1), device=x.device, dtype=x.dtype)
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x_padded = torch.cat([zero_pad, x], dim=-1)
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x_padded = x_padded.view(*x.size()[:2], x.size(3) + 1, x.size(2))
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x = x_padded[:, :, 1:].view_as(x)[
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:, :, :, : x.size(-1) // 2 + 1
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] # only keep the positions from 0 to time2
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return x
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def forward_attention(self, value, scores, mask):
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scores = scores + mask
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self.attn = torch.softmax(scores, dim=-1)
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context_layer = torch.matmul(self.attn, value) # (batch, head, time1, d_k)
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context_layer = context_layer.permute(0, 2, 1, 3).contiguous()
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new_context_layer_shape = context_layer.size()[:-2] + (self.all_head_size,)
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context_layer = context_layer.view(new_context_layer_shape)
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return self.linear_out(context_layer) # (batch, time1, d_model)
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