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| # Copyright 2017 The TensorFlow Authors All Rights Reserved. | |
| # | |
| # Licensed under the Apache License, Version 2.0 (the "License"); | |
| # you may not use this file except in compliance with the License. | |
| # You may obtain a copy of the License at | |
| # | |
| # http://www.apache.org/licenses/LICENSE-2.0 | |
| # | |
| # Unless required by applicable law or agreed to in writing, software | |
| # distributed under the License is distributed on an "AS IS" BASIS, | |
| # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| # See the License for the specific language governing permissions and | |
| # limitations under the License. | |
| # ============================================================================== | |
| """Set of blocks related to entropy coding.""" | |
| import math | |
| import tensorflow as tf | |
| import block_base | |
| # pylint does not recognize block_base.BlockBase.__call__(). | |
| # pylint: disable=not-callable | |
| class CodeLength(block_base.BlockBase): | |
| """Theoretical bound for a code length given a probability distribution. | |
| """ | |
| def __init__(self, name=None): | |
| super(CodeLength, self).__init__(name) | |
| def _Apply(self, c, p): | |
| """Theoretical bound of the coded length given a probability distribution. | |
| Args: | |
| c: The binary codes. Belong to {0, 1}. | |
| p: The probability of: P(code==+1) | |
| Returns: | |
| The average code length. | |
| Note: the average code length can be greater than 1 bit (e.g. when | |
| encoding the least likely symbol). | |
| """ | |
| entropy = ((1.0 - c) * tf.log(1.0 - p) + c * tf.log(p)) / (-math.log(2)) | |
| entropy = tf.reduce_mean(entropy) | |
| return entropy | |