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# Licensed under the Apache License, Version 2.0 (the "License");
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#     http://www.apache.org/licenses/LICENSE-2.0
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"""Utils for MAE."""

import math
import tensorflow as tf
from official.modeling import tf_utils


# TODO(frederickliu): Move this to vision ops and add tests.
def position_embedding_sine(attention_mask,
                            num_pos_features=256,
                            temperature=10000.,
                            normalize=True,
                            scale=2 * math.pi):
  """Sine-based positional embeddings for 2D images.

  Args:
    attention_mask: a `bool` Tensor specifying the size of the input image to
      the Transformer and which elements are padded, of size [batch_size,
      height, width]
    num_pos_features: a `int` specifying the number of positional features,
      should be equal to the hidden size of the Transformer network
    temperature: a `float` specifying the temperature of the positional
      embedding. Any type that is converted to a `float` can also be accepted.
    normalize: a `bool` determining whether the positional embeddings should be
      normalized between [0, scale] before application of the sine and cos
      functions.
    scale: a `float` if normalize is True specifying the scale embeddings before
      application of the embedding function.

  Returns:
    embeddings: a `float` tensor of the same shape as input_tensor specifying
      the positional embeddings based on sine features.
  """
  if num_pos_features % 2 != 0:
    raise ValueError(
        "Number of embedding features (num_pos_features) must be even when "
        "column and row embeddings are concatenated.")
  num_pos_features = num_pos_features // 2

  # Produce row and column embeddings based on total size of the image
  # <tf.float>[batch_size, height, width]
  attention_mask = tf.cast(attention_mask, tf.float32)
  row_embedding = tf.cumsum(attention_mask, 1)
  col_embedding = tf.cumsum(attention_mask, 2)

  if normalize:
    eps = 1e-6
    row_embedding = row_embedding / (row_embedding[:, -1:, :] + eps) * scale
    col_embedding = col_embedding / (col_embedding[:, :, -1:] + eps) * scale

  dim_t = tf.range(num_pos_features, dtype=row_embedding.dtype)
  dim_t = tf.pow(temperature, 2 * (dim_t // 2) / num_pos_features)

  # Creates positional embeddings for each row and column position
  # <tf.float>[batch_size, height, width, num_pos_features]
  pos_row = tf.expand_dims(row_embedding, -1) / dim_t
  pos_col = tf.expand_dims(col_embedding, -1) / dim_t
  pos_row = tf.stack(
      [tf.sin(pos_row[:, :, :, 0::2]),
       tf.cos(pos_row[:, :, :, 1::2])], axis=4)
  pos_col = tf.stack(
      [tf.sin(pos_col[:, :, :, 0::2]),
       tf.cos(pos_col[:, :, :, 1::2])], axis=4)

  # final_shape = pos_row.shape.as_list()[:3] + [-1]
  final_shape = tf_utils.get_shape_list(pos_row)[:3] + [-1]
  pos_row = tf.reshape(pos_row, final_shape)
  pos_col = tf.reshape(pos_col, final_shape)
  output = tf.concat([pos_row, pos_col], -1)

  embeddings = tf.cast(output, tf.float32)
  return embeddings