text: /* Copyright 2019 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.
  ==============================================================================*/
  
  #include "tensorflow/lite/micro/examples/micro_speech/micro_features/micro_features_generator.h"
  
  #include <cmath>
  #include <cstring>
  
  #include "tensorflow/lite/experimental/microfrontend/lib/frontend.h"
  #include "tensorflow/lite/experimental/microfrontend/lib/frontend_util.h"
  #include "tensorflow/lite/micro/examples/micro_speech/micro_features/micro_model_settings.h"
  
  // Configure FFT to output 16 bit fixed point.
  #define FIXED_POINT 16
  
  namespace {
  
  FrontendState g_micro_features_state;
  bool g_is_first_time = true;
  
  }  // namespace
  
  TfLiteStatus InitializeMicroFeatures(tflite::ErrorReporter* error_reporter) {
    FrontendConfig config;
    config.window.size_ms = kFeatureSliceDurationMs;
    config.window.step_size_ms = kFeatureSliceStrideMs;
    config.noise_reduction.smoothing_bits = 10;
    config.filterbank.num_channels = kFeatureSliceSize;
    config.filterbank.lower_band_limit = 125.0;
    config.filterbank.upper_band_limit = 7500.0;
    config.noise_reduction.smoothing_bits = 10;
    config.noise_reduction.even_smoothing = 0.025;
    config.noise_reduction.odd_smoothing = 0.06;
    config.noise_reduction.min_signal_remaining = 0.05;
    config.pcan_gain_control.enable_pcan = 1;
    config.pcan_gain_control.strength = 0.95;
    config.pcan_gain_control.offset = 80.0;
    config.pcan_gain_control.gain_bits = 21;
    config.log_scale.enable_log = 1;
    config.log_scale.scale_shift = 6;
    if (!FrontendPopulateState(&config, &g_micro_features_state,
                               kAudioSampleFrequency)) {
      error_reporter->Report("FrontendPopulateState() failed");
      return kTfLiteError;
    }
    g_is_first_time = true;
    return kTfLiteOk;
  }
  
  // This is not exposed in any header, and is only used for testing, to ensure
  // that the state is correctly set up before generating results.
  void SetMicroFeaturesNoiseEstimates(const uint32_t* estimate_presets) {
    for (int i = 0; i < g_micro_features_state.filterbank.num_channels; ++i) {
      g_micro_features_state.noise_reduction.estimate[i] = estimate_presets[i];
    }
  }
  
  TfLiteStatus GenerateMicroFeatures(tflite::ErrorReporter* error_reporter,
                                     const int16_t* input, int input_size,
                                     int output_size, uint8_t* output,
                                     size_t* num_samples_read) {
    const int16_t* frontend_input;
    if (g_is_first_time) {
      frontend_input = input;
      g_is_first_time = false;
    } else {
      frontend_input = input + 160;
    }
    FrontendOutput frontend_output = FrontendProcessSamples(
        &g_micro_features_state, frontend_input, input_size, num_samples_read);
  
    for (int i = 0; i < frontend_output.size; ++i) {
      // These scaling values are derived from those used in input_data.py in the
      // training pipeline.
      constexpr int32_t value_scale = (10 * 255);
      constexpr int32_t value_div = (256 * 26);
      int32_t value =
          ((frontend_output.values[i] * value_scale) + (value_div / 2)) /
          value_div;
      if (value < 0) {
        value = 0;
      }
      if (value > 255) {
        value = 255;
      }
      output[i] = value;
    }
  
    return kTfLiteOk;
  }
  