code: def standard_normal_density(x, x_mask, reduce_sum=False):
      """Return standard normal distribution with same shape as x."""
      log_probs = -0.5 * (x**2 + math.log(math.pi * 2.0))
      if reduce_sum:
          log_probs = reduce_mean_over_bl_sum_over_c(log_probs, x_mask)
      else:
          log_probs = reduce_sum_over_lc(log_probs, x_mask)
      return log_probs
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import copy
  import math
  from tensor2tensor.layers import common_attention
  from tensor2tensor.layers import common_layers
  from tensor2tensor.models.transformer import transformer_decoder_layer
  import tensorflow.compat.v1
  import tensorflow_probability
label_desc: Use image node_id 11 for calling a global function with example usage: standard_normal_density(x, x_mask, reduce_sum) and returns: log_probs