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/*
* Copyright (c) 2022 Project Nayuki. (MIT License)
*
* 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.
*
* SPDX-License-Identifier: Apache-2.0
*/
#include <math.h>
#include <stdint.h>
#include <stdlib.h>
#include "fast-dct-fft.h"
#include "../returntypes.hpp"
#include "../numpy.hpp"
#include "../memory.hpp"
#ifndef M_PI
#define M_PI 3.14159265358979323846264338327950288
#endif // M_PI
// DCT type II, unscaled
int ei::dct::transform(float vector[], size_t len) {
const size_t fft_data_out_size = (len / 2 + 1) * sizeof(ei::fft_complex_t);
const size_t fft_data_in_size = len * sizeof(float);
// Allocate KissFFT input / output buffer
fft_complex_t *fft_data_out =
(ei::fft_complex_t*)ei_dsp_calloc(fft_data_out_size, 1);
if (!fft_data_out) {
return ei::EIDSP_OUT_OF_MEM;
}
float *fft_data_in = (float*)ei_dsp_calloc(fft_data_in_size, 1);
if (!fft_data_in) {
ei_dsp_free(fft_data_out, fft_data_out_size);
return ei::EIDSP_OUT_OF_MEM;
}
// Preprocess the input buffer with the data from the vector
size_t halfLen = len / 2;
for (size_t i = 0; i < halfLen; i++) {
fft_data_in[i] = vector[i * 2];
fft_data_in[len - 1 - i] = vector[i * 2 + 1];
}
if (len % 2 == 1) {
fft_data_in[halfLen] = vector[len - 1];
}
int r = ei::numpy::rfft(fft_data_in, len, fft_data_out, (len / 2 + 1), len);
if (r != 0) {
ei_dsp_free(fft_data_in, fft_data_in_size);
ei_dsp_free(fft_data_out, fft_data_out_size);
return r;
}
size_t i = 0;
for (; i < len / 2 + 1; i++) {
float temp = i * M_PI / (len * 2);
vector[i] = fft_data_out[i].r * cos(temp) + fft_data_out[i].i * sin(temp);
}
//take advantage of hermetian symmetry to calculate remainder of signal
for (; i < len; i++) {
float temp = i * M_PI / (len * 2);
int conj_idx = len-i;
// second half bins not calculated would have just been the conjugate of the first half (note minus of imag)
vector[i] = fft_data_out[conj_idx].r * cos(temp) - fft_data_out[conj_idx].i * sin(temp);
}
ei_dsp_free(fft_data_in, fft_data_in_size);
ei_dsp_free(fft_data_out, fft_data_out_size);
return 0;
} |