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922b66abdb
Define and move constants in nanovna.h, and use it Fix command 'marker' - display marker freq (not current freq)
91 lines
2.9 KiB
C
91 lines
2.9 KiB
C
/*
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* fft.h is Based on
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* Free FFT and convolution (C)
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*
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* Copyright (c) 2019 Project Nayuki. (MIT License)
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* https://www.nayuki.io/page/free-small-fft-in-multiple-languages
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of
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* this software and associated documentation files (the "Software"), to deal in
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* the Software without restriction, including without limitation the rights to
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* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
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* the Software, and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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* - The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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* - The Software is provided "as is", without warranty of any kind, express or
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* implied, including but not limited to the warranties of merchantability,
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* fitness for a particular purpose and noninfringement. In no event shall the
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* authors or copyright holders be liable for any claim, damages or other
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* liability, whether in an action of contract, tort or otherwise, arising from,
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* out of or in connection with the Software or the use or other dealings in the
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* Software.
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*/
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#include <math.h>
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#include <stdint.h>
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static uint16_t reverse_bits(uint16_t x, int n) {
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uint16_t result = 0;
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int i;
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for (i = 0; i < n; i++, x >>= 1)
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result = (result << 1) | (x & 1U);
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return result;
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}
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/***
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* dir = forward: 0, inverse: 1
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* https://www.nayuki.io/res/free-small-fft-in-multiple-languages/fft.c
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*/
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static void fft256(float array[][2], const uint8_t dir) {
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const uint16_t n = 256;
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const uint8_t levels = 8; // log2(n)
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const uint8_t real = dir & 1;
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const uint8_t imag = ~real & 1;
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uint16_t i;
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uint16_t size;
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for (i = 0; i < n; i++) {
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uint16_t j = reverse_bits(i, levels);
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if (j > i) {
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float temp = array[i][real];
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array[i][real] = array[j][real];
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array[j][real] = temp;
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temp = array[i][imag];
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array[i][imag] = array[j][imag];
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array[j][imag] = temp;
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}
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}
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// Cooley-Tukey decimation-in-time radix-2 FFT
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for (size = 2; size <= n; size *= 2) {
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uint16_t halfsize = size / 2;
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uint16_t tablestep = n / size;
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uint16_t i;
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for (i = 0; i < n; i += size) {
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uint16_t j, k;
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for (j = i, k = 0; j < i + halfsize; j++, k += tablestep) {
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uint16_t l = j + halfsize;
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float tpre = array[l][real] * cos(2 * VNA_PI * k / 256) + array[l][imag] * sin(2 * VNA_PI * k / 256);
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float tpim = -array[l][real] * sin(2 * VNA_PI * k / 256) + array[l][imag] * cos(2 * VNA_PI * k / 256);
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array[l][real] = array[j][real] - tpre;
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array[l][imag] = array[j][imag] - tpim;
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array[j][real] += tpre;
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array[j][imag] += tpim;
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}
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}
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if (size == n) // Prevent overflow in 'size *= 2'
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break;
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}
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}
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static inline void fft256_forward(float array[][2]) {
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fft256(array, 0);
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}
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static inline void fft256_inverse(float array[][2]) {
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fft256(array, 1);
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}
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