| /* 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 "signal/src/filter_bank.h" |
| |
| namespace tflite { |
| namespace tflm_signal { |
| |
| void FilterbankAccumulateChannels(const FilterbankConfig* config, |
| const uint32_t* input, uint64_t* output) { |
| // With a log mel filterbank, the energy at each frequency gets added to |
| // two adjacent filterbank filters/channels. |
| // For the first filter bank channel, its energy is first multiplied by |
| // some weight 'w', then gets accumulated. |
| // For the subsequent filter bank, its power is first multiplied by 1-'w' |
| // (called unweight here), then gets accumulated. |
| // For this reason, we need to calculate (config->num_channels + 1) output |
| // where element 0 is only used as scratch storage for the unweights of |
| // element 1 (channel 0). The caller should discard element 0. |
| // Writing the code like this doesn't save multiplications, but it lends |
| // itself better to optimization, because input[freq_start + j] only needs |
| // to be loaded once. |
| uint64_t weight_accumulator = 0; |
| uint64_t unweight_accumulator = 0; |
| for (int i = 0; i < config->num_channels + 1; i++) { |
| const int16_t freq_start = config->channel_frequency_starts[i]; |
| const int16_t weight_start = config->channel_weight_starts[i]; |
| for (int j = 0; j < config->channel_widths[i]; ++j) { |
| weight_accumulator += config->weights[weight_start + j] * |
| static_cast<uint64_t>(input[freq_start + j]); |
| unweight_accumulator += config->unweights[weight_start + j] * |
| static_cast<uint64_t>(input[freq_start + j]); |
| } |
| output[i] = weight_accumulator; |
| weight_accumulator = unweight_accumulator; |
| unweight_accumulator = 0; |
| } |
| } |
| |
| } // namespace tflm_signal |
| } // namespace tflite |