src/main/common/sdft.h

   1 /*
   2  * This file is part of Cleanflight and Betaflight.
   3  *
   4  * Cleanflight and Betaflight are free software. You can redistribute
   5  * this software and/or modify this software under the terms of the
   6  * GNU General Public License as published by the Free Software
   7  * Foundation, either version 3 of the License, or (at your option)
   8  * any later version.
   9  *
  10  * Cleanflight and Betaflight are distributed in the hope that they
  11  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  12  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  13  * See the GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this software.
  17  *
  18  * If not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21  // Implementation of a Sliding Discrete Fourier Transform (SDFT).
  22  // Complexity for calculating frequency spectrum with N bins is O(N).
  23
  24 #pragma once
  25
  26 #include <stdint.h>
  27 #include <complex.h>
  28 #undef I  // avoid collision of imaginary unit I with variable I in pid.h
  29 typedef float complex complex_t; // Better readability for type "float complex"
  30
  31 #define SDFT_SAMPLE_SIZE 72
  32 #define SDFT_BIN_COUNT   (SDFT_SAMPLE_SIZE / 2)
  33
  34 typedef struct sdft_s {
  35
  36     int idx;                           // circular buffer index
  37     int startBin;
  38     int endBin;
  39     int batchSize;
  40     int numBatches;
  41     float samples[SDFT_SAMPLE_SIZE];   // circular buffer
  42     complex_t data[SDFT_BIN_COUNT];    // complex frequency spectrum
  43
  44 } sdft_t;
  45
  46 void sdftInit(sdft_t *sdft, const int startBin, const int endBin, const int numBatches);
  47 void sdftPush(sdft_t *sdft, const float sample);
  48 void sdftPushBatch(sdft_t *sdft, const float sample, const int batchIdx);
  49 void sdftMagSq(const sdft_t *sdft, float *output);
  50 void sdftMagnitude(const sdft_t *sdft, float *output);
  51 void sdftWinSq(const sdft_t *sdft, float *output);
  52 void sdftWindow(const sdft_t *sdft, float *output);