TensorflowLiteMicro/tensorflow/lite/experimental/microfrontend/lib/frontend.c

/* Copyright 2018 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/experimental/microfrontend/lib/frontend.h"

#include "tensorflow/lite/experimental/microfrontend/lib/bits.h"

struct FrontendOutput FrontendProcessSamples(struct FrontendState* state,
                                             const int16_t* samples,
                                             size_t num_samples,
                                             size_t* num_samples_read) {
  struct FrontendOutput output;
  output.values = NULL;
  output.size = 0;

  // Try to apply the window - if it fails, return and wait for more data.
  if (!WindowProcessSamples(&state->window, samples, num_samples,
                            num_samples_read)) {
    return output;
  }

  // Apply the FFT to the window's output (and scale it so that the fixed point
  // FFT can have as much resolution as possible).
  int input_shift =
      15 - MostSignificantBit32(state->window.max_abs_output_value);
  FftCompute(&state->fft, state->window.output, input_shift);

  // We can re-ruse the fft's output buffer to hold the energy.
  int32_t* energy = (int32_t*)state->fft.output;

  FilterbankConvertFftComplexToEnergy(&state->filterbank, state->fft.output,
                                      energy);

  FilterbankAccumulateChannels(&state->filterbank, energy);
  uint32_t* scaled_filterbank = FilterbankSqrt(&state->filterbank, input_shift);

  // Apply noise reduction.
  NoiseReductionApply(&state->noise_reduction, scaled_filterbank);

  if (state->pcan_gain_control.enable_pcan) {
    PcanGainControlApply(&state->pcan_gain_control, scaled_filterbank);
  }

  // Apply the log and scale.
  int correction_bits =
      MostSignificantBit32(state->fft.fft_size) - 1 - (kFilterbankBits / 2);
  uint16_t* logged_filterbank =
      LogScaleApply(&state->log_scale, scaled_filterbank,
                    state->filterbank.num_channels, correction_bits);

  output.size = state->filterbank.num_channels;
  output.values = logged_filterbank;
  return output;
}

void FrontendReset(struct FrontendState* state) {
  WindowReset(&state->window);
  FftReset(&state->fft);
  FilterbankReset(&state->filterbank);
  NoiseReductionReset(&state->noise_reduction);
}