def _get_symbols_to_logits_fn(self, max_decode_length, training):
"""Returns a decoding function that calculates logits of the next tokens."""
pos_layer = position_embedding.RelativePositionEmbedding(
hidden_size=self.params["hidden_size"],
length=max_decode_length + 1)
timing_signal = pos_layer(None)
timing_signal = tf.cast(timing_signal, self.params["dtype"])
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
max_decode_length, dtype=self.params["dtype"])
# TODO(b/139770046): Refactor code with better naming of i.
def symbols_to_logits_fn(ids, i, cache):
"""Generate logits for next potential IDs.
Args:
ids: Current decoded sequences. int tensor with shape [batch_size *
beam_size, i + 1].
i: Loop index.
cache: dictionary of values storing the encoder output, encoder-decoder
attention bias, and previous decoder attention values.
Returns:
Tuple of
(logits with shape [batch_size * beam_size, vocab_size],
updated cache values)
"""
# Set decoder input to the last generated IDs
decoder_input = ids[:, -1:]
# Preprocess decoder input by getting embeddings and adding timing signal.
decoder_input = self.embedding_softmax_layer(decoder_input)
if self.params["padded_decode"]:
timing_signal_shape = timing_signal.shape.as_list()
decoder_input += tf.slice(timing_signal, [i, 0],
[1, timing_signal_shape[1]])
bias_shape = decoder_self_attention_bias.shape.as_list()
self_attention_bias = tf.slice(
decoder_self_attention_bias, [0, 0, i, 0],
[bias_shape[0], bias_shape[1], 1, bias_shape[3]])
else:
decoder_input += timing_signal[i:i + 1]
self_attention_bias = decoder_self_attention_bias[:, :, i:i + 1, :i + 1]
decoder_outputs = self.decoder_stack(
decoder_input,
cache.get("encoder_outputs"),
self_attention_bias,
cache.get("encoder_decoder_attention_bias"),
training=training,
cache=cache,
decode_loop_step=i if self.params["padded_decode"] else None)
logits = self.embedding_softmax_layer(decoder_outputs, mode="linear")
logits = tf.squeeze(logits, axis=[1])
return logits, cache
return symbols_to_logits_fn
def decode(self, targets: tf.Tensor, reminder_outputs: tf.Tensor,
attention_bias: tf.Tensor, training: bool) -> tf.Tensor:
with tf.name_scope("decode"):
# Prepare inputs to decoder layers by shifting targets, adding positional
# encoding and applying dropout.
decoder_inputs = self.embedding_softmax_layer(targets)
decoder_inputs = tf.cast(decoder_inputs, self.params["dtype"])
attention_bias = tf.cast(attention_bias, self.params["dtype"])
with tf.name_scope("add_pos_encoding"):
length = tf.shape(decoder_inputs)[1]
pos_encoding = self.position_embedding(decoder_inputs)
pos_encoding = tf.cast(pos_encoding, self.params["dtype"])
decoder_inputs += pos_encoding
if training:
decoder_inputs = tf.nn.dropout(
decoder_inputs,
rate=self.params["layer_postprocess_dropout"])
# Run values
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
length, dtype=self.params["dtype"])
outputs = self.decoder_stack(decoder_inputs,
reminder_outputs,
decoder_self_attention_bias,
attention_bias,
training=training)
logits = self.embedding_softmax_layer(outputs, mode="linear")
logits = tf.cast(logits, tf.float32)
return logits
def test_get_decoder_self_attention_bias(self):
length = 5
bias = model_utils.get_decoder_self_attention_bias(length)
self.assertAllEqual(
[[[[0, NEG_INF, NEG_INF, NEG_INF, NEG_INF],
[0, 0, NEG_INF, NEG_INF, NEG_INF], [0, 0, 0, NEG_INF, NEG_INF],
[0, 0, 0, 0, NEG_INF], [0, 0, 0, 0, 0]]]], bias)
def decode(self, targets, encoder_outputs, attention_bias, training):
"""Generate logits for each value in the target sequence.
Args:
targets: target values for the output sequence. int tensor with shape
[batch_size, target_length]
encoder_outputs: continuous representation of input sequence. float tensor
with shape [batch_size, input_length, hidden_size]
attention_bias: float tensor with shape [batch_size, 1, 1, input_length]
training: boolean, whether in training mode or not.
Returns:
float32 tensor with shape [batch_size, target_length, vocab_size]
"""
with tf.name_scope("decode"):
# Prepare inputs to decoder layers by shifting targets, adding positional
# encoding and applying dropout.
decoder_inputs = self.embedding_softmax_layer(targets)
decoder_inputs = tf.cast(decoder_inputs, self.params["dtype"])
attention_bias = tf.cast(attention_bias, self.params["dtype"])
with tf.name_scope("shift_targets"):
# Shift targets to the right, and remove the last element
decoder_inputs = tf.pad(decoder_inputs,
[[0, 0], [1, 0], [0, 0]])[:, :-1, :]
with tf.name_scope("add_pos_encoding"):
length = tf.shape(decoder_inputs)[1]
pos_layer = position_embedding.RelativePositionEmbedding(
hidden_size=self.params["hidden_size"])
pos_encoding = pos_layer(decoder_inputs)
pos_encoding = tf.cast(pos_encoding, self.params["dtype"])
decoder_inputs += pos_encoding
if training:
decoder_inputs = tf.nn.dropout(
decoder_inputs, rate=self.params["layer_postprocess_dropout"])
# Run values
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
length, dtype=self.params["dtype"])
outputs = self.decoder_stack(
decoder_inputs,
encoder_outputs,
decoder_self_attention_bias,
attention_bias,
training=training)
logits = self.embedding_softmax_layer(outputs, mode="linear")
logits = tf.cast(logits, tf.float32)
return logits
def _get_symbols_to_logits_fn(self, max_decode_length):
"""Returns a decoding function that calculates logits of the next tokens."""
timing_signal = model_utils.get_position_encoding(
max_decode_length + 1, self.params["hidden_size"])
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
max_decode_length)
def symbols_to_logits_fn(ids, i, cache):
"""Generate logits for next potential IDs.
Args:
ids: Current decoded sequences.
int tensor with shape [batch_size * beam_size, i + 1]
i: Loop index
cache: dictionary of values storing the encoder output, encoder-decoder
attention bias, and previous decoder attention values.
Returns:
Tuple of
(logits with shape [batch_size * beam_size, vocab_size],
updated cache values)
"""
# Set decoder input to the last generated IDs
decoder_input = ids[:, -1:]
# Preprocess decoder input by getting embeddings and adding timing signal.
decoder_input = self.embedding_softmax_layer(decoder_input)
decoder_input += timing_signal[i:i + 1]
self_attention_bias = decoder_self_attention_bias[:, :,
i:i + 1, :i + 1]
decoder_outputs = self.decoder_stack(
decoder_input,
cache.get("encoder_outputs"), self_attention_bias,
cache.get("encoder_decoder_attention_bias"), cache)
logits = self.embedding_softmax_layer.linear(decoder_outputs)
logits = tf.squeeze(logits, axis=[1])
return logits, cache
return symbols_to_logits_fn
def decode(self, targets, encoder_outputs, attention_bias):
"""Generate logits for each value in the target sequence.
Args:
targets: target values for the output sequence.
int tensor with shape [batch_size, target_length]
encoder_outputs: continuous representation of input sequence.
float tensor with shape [batch_size, input_length, hidden_size]
attention_bias: float tensor with shape [batch_size, 1, 1, input_length]
Returns:
float32 tensor with shape [batch_size, target_length, vocab_size]
"""
with tf.name_scope("decode"):
# Prepare inputs to decoder layers by shifting targets, adding positional
# encoding and applying dropout.
decoder_inputs = self.embedding_softmax_layer(targets)
with tf.name_scope("shift_targets"):
# Shift targets to the right, and remove the last element
decoder_inputs = tf.pad(decoder_inputs,
[[0, 0], [1, 0], [0, 0]])[:, :-1, :]
with tf.name_scope("add_pos_encoding"):
length = tf.shape(decoder_inputs)[1]
decoder_inputs += model_utils.get_position_encoding(
length, self.params["hidden_size"])
if self.train:
decoder_inputs = tf.nn.dropout(
decoder_inputs,
1 - self.params["layer_postprocess_dropout"])
# Run values
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
length)
outputs = self.decoder_stack(decoder_inputs, encoder_outputs,
decoder_self_attention_bias,
attention_bias)
logits = self.embedding_softmax_layer.linear(outputs)
return logits
def get_attention_bias(input_tensor,
bias_type,
padding_value=0,
max_length=None):
"""A helper function to get various attention bias tensors."""
if bias_type not in ("single_cross", "multi_cross", "decoder_self"):
raise ValueError("Invalid attention bias type: %s" % bias_type)
if bias_type == "single_cross":
length = tf_utils.get_shape_list(input_tensor, expected_rank=2)[1]
bias = transformer_utils.get_padding_bias(input_tensor,
padding_value=padding_value)
elif bias_type == "multi_cross":
length = tf_utils.get_shape_list(input_tensor, expected_rank=3)[2]
padding = transformer_utils.get_padding(input_tensor,
padding_value=padding_value)
bias = padding * -1e9
else:
if max_length is not None:
length = max_length
else:
length = tf_utils.get_shape_list(input_tensor, expected_rank=2)[1]
bias = transformer_utils.get_decoder_self_attention_bias(length)
return tf.where(bias < 0, tf.zeros_like(bias), tf.ones_like(bias))
def _get_symbols_to_logits_fn(self, max_decode_length):
"""Returns a decoding function that calculates logits of the next tokens."""
timing_signal = self.position_embedding(inputs=None,
length=max_decode_length + 1)
timing_signal = tf.cast(timing_signal, self._dtype)
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
max_decode_length, dtype=self._dtype)
def symbols_to_logits_fn(ids, i, cache):
"""Generate logits for next potential IDs.
Args:
ids: Current decoded sequences. int tensor with shape [batch_size *
beam_size, i + 1].
i: Loop index.
cache: dictionary of values storing the encoder output, encoder-decoder
attention bias, and previous decoder attention values.
Returns:
Tuple of
(logits with shape [batch_size * beam_size, vocab_size],
updated cache values)
"""
# Set decoder input to the last generated IDs
decoder_input = ids[:, -1:]
# Preprocess decoder input by getting embeddings and adding timing signal.
# decoder_input = self.embedding_softmax_layer(decoder_input)
source_decoder_input = decoder_input
decoder_input = self.embedding_lookup(decoder_input)
embedding_mask = tf.cast(tf.not_equal(source_decoder_input, 0),
self.embedding_lookup.embeddings.dtype)
decoder_input *= tf.expand_dims(embedding_mask, -1)
if self._padded_decode:
timing_signal_shape = timing_signal.shape.as_list()
decoder_input += tf.slice(timing_signal, [i, 0],
[1, timing_signal_shape[1]])
bias_shape = decoder_self_attention_bias.shape.as_list()
self_attention_bias = tf.slice(
decoder_self_attention_bias, [0, 0, i, 0],
[bias_shape[0], bias_shape[1], 1, bias_shape[3]])
else:
decoder_input += timing_signal[i:i + 1]
self_attention_bias = decoder_self_attention_bias[:, :, i:i +
1, :i + 1]
decoder_shape = tf_utils.get_shape_list(decoder_input,
expected_rank=3)
batch_size = decoder_shape[0]
decoder_length = decoder_shape[1]
attention_bias = cache.get("encoder_decoder_attention_bias")
attention_bias = tf.where(attention_bias < 0,
tf.zeros_like(attention_bias),
tf.ones_like(attention_bias))
attention_bias = tf.squeeze(attention_bias, axis=[1])
attention_mask = tf.tile(attention_bias, [1, decoder_length, 1])
self_attention_bias = tf.where(self_attention_bias < 0,
tf.zeros_like(self_attention_bias),
tf.ones_like(self_attention_bias))
self_attention_bias = tf.squeeze(self_attention_bias, axis=[1])
self_attention_mask = tf.tile(self_attention_bias,
[batch_size, 1, 1])
decoder_outputs = self.decoder_layer(
decoder_input,
cache.get("encoder_outputs"),
memory_mask=self_attention_mask,
target_mask=attention_mask,
cache=cache,
decode_loop_step=i if self._padded_decode else None)
logits = self._embedding_linear(self.embedding_lookup.embeddings,
decoder_outputs)
logits = tf.squeeze(logits, axis=[1])
return logits, cache
return symbols_to_logits_fn
