from typing import Any
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from typing import List
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from typing import Tuple
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import torch
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import torch.nn as nn
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from funasr.modules.embedding import PositionalEncoding
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from funasr.models.encoder.transformer_encoder import TransformerEncoder_s0 as Encoder
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from funasr.modules.mask import subsequent_mask
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from funasr.train.abs_model import AbsLM
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class TransformerLM(AbsLM):
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def __init__(
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self,
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vocab_size: int,
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pos_enc: str = None,
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embed_unit: int = 128,
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att_unit: int = 256,
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head: int = 2,
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unit: int = 1024,
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layer: int = 4,
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dropout_rate: float = 0.5,
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):
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super().__init__()
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if pos_enc == "sinusoidal":
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pos_enc_class = PositionalEncoding
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elif pos_enc is None:
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def pos_enc_class(*args, **kwargs):
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return nn.Sequential() # indentity
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else:
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raise ValueError(f"unknown pos-enc option: {pos_enc}")
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self.embed = nn.Embedding(vocab_size, embed_unit)
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self.encoder = Encoder(
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idim=embed_unit,
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attention_dim=att_unit,
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attention_heads=head,
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linear_units=unit,
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num_blocks=layer,
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dropout_rate=dropout_rate,
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input_layer="linear",
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pos_enc_class=pos_enc_class,
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)
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self.decoder = nn.Linear(att_unit, vocab_size)
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def _target_mask(self, ys_in_pad):
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ys_mask = ys_in_pad != 0
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m = subsequent_mask(ys_mask.size(-1), device=ys_mask.device).unsqueeze(0)
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return ys_mask.unsqueeze(-2) & m
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def forward(self, input: torch.Tensor, hidden: None) -> Tuple[torch.Tensor, None]:
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"""Compute LM loss value from buffer sequences.
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Args:
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input (torch.Tensor): Input ids. (batch, len)
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hidden (torch.Tensor): Target ids. (batch, len)
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"""
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x = self.embed(input)
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mask = self._target_mask(input)
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h, _ = self.encoder(x, mask)
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y = self.decoder(h)
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return y, None
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def score(
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self, y: torch.Tensor, state: Any, x: torch.Tensor
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) -> Tuple[torch.Tensor, Any]:
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"""Score new token.
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Args:
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y (torch.Tensor): 1D torch.int64 prefix tokens.
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state: Scorer state for prefix tokens
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x (torch.Tensor): encoder feature that generates ys.
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Returns:
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tuple[torch.Tensor, Any]: Tuple of
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torch.float32 scores for next token (vocab_size)
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and next state for ys
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"""
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y = y.unsqueeze(0)
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h, _, cache = self.encoder.forward_one_step(
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self.embed(y), self._target_mask(y), cache=state
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)
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h = self.decoder(h[:, -1])
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logp = h.log_softmax(dim=-1).squeeze(0)
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return logp, cache
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def batch_score(
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self, ys: torch.Tensor, states: List[Any], xs: torch.Tensor
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) -> Tuple[torch.Tensor, List[Any]]:
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"""Score new token batch.
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Args:
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ys (torch.Tensor): torch.int64 prefix tokens (n_batch, ylen).
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states (List[Any]): Scorer states for prefix tokens.
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xs (torch.Tensor):
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The encoder feature that generates ys (n_batch, xlen, n_feat).
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Returns:
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tuple[torch.Tensor, List[Any]]: Tuple of
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batchfied scores for next token with shape of `(n_batch, vocab_size)`
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and next state list for ys.
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"""
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# merge states
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n_batch = len(ys)
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n_layers = len(self.encoder.encoders)
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if states[0] is None:
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batch_state = None
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else:
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# transpose state of [batch, layer] into [layer, batch]
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batch_state = [
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torch.stack([states[b][i] for b in range(n_batch)])
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for i in range(n_layers)
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]
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# batch decoding
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h, _, states = self.encoder.forward_one_step(
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self.embed(ys), self._target_mask(ys), cache=batch_state
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)
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h = self.decoder(h[:, -1])
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logp = h.log_softmax(dim=-1)
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# transpose state of [layer, batch] into [batch, layer]
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state_list = [[states[i][b] for i in range(n_layers)] for b in range(n_batch)]
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return logp, state_list
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