/**
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* Copyright (c) 2022 Xiaomi Corporation (authors: Fangjun Kuang)
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*
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* See LICENSE for clarification regarding multiple authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// This file is copied/modified from kaldi/src/feat/feature-functions.cc
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#include "kaldi-native-fbank/csrc/feature-functions.h"
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#include <cstdint>
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#include <vector>
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namespace knf {
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void ComputePowerSpectrum(std::vector<float> *complex_fft) {
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int32_t dim = complex_fft->size();
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// now we have in complex_fft, first half of complex spectrum
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// it's stored as [real0, realN/2, real1, im1, real2, im2, ...]
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float *p = complex_fft->data();
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int32_t half_dim = dim / 2;
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float first_energy = p[0] * p[0];
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float last_energy = p[1] * p[1]; // handle this special case
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for (int32_t i = 1; i < half_dim; ++i) {
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float real = p[i * 2];
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float im = p[i * 2 + 1];
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p[i] = real * real + im * im;
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}
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p[0] = first_energy;
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p[half_dim] = last_energy; // Will actually never be used, and anyway
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// if the signal has been bandlimited sensibly this should be zero.
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}
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} // namespace knf
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