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/* -*- c++ -*- */
/*
* Copyright 2019 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifndef INCLUDED_FFT_FFT_SHIFT_H
#define INCLUDED_FFT_FFT_SHIFT_H
#include <algorithm>
#include <cassert>
#include <vector>
namespace gr {
namespace fft {
/*! \brief reorder FFT results which are ordered from 0 to 1 in normalized frequency
* to -0.5 to 0.5 by cyclic shift
*/
template<typename T>
class fft_shift {
public:
fft_shift(size_t fft_length)
: d_fftlen(fft_length)
, d_lenpos(fft_length/2 + (fft_length%2))
, d_lenneg(fft_length/2)
, d_buf(fft_length) {}
/*! performs the cyclic shift on a vector v
*/
void shift(std::vector<T>& v) {
shift(&v.front(), v.size());
}
/*! performs the cyclic shift on an array
*/
void shift(T* data, size_t fft_len) {
resize(fft_len);
std::copy_n(data, d_lenpos, d_buf.begin());
std::copy_n(data+d_lenpos, d_lenneg, data);
std::copy_n(d_buf.begin(), d_lenpos, data+d_lenneg);
}
/*! if needed adjusts the buffer size to a new fft length
*/
void resize(size_t fft_length) {
if (d_fftlen == fft_length)
return;
d_fftlen = fft_length;
d_lenpos = d_fftlen/2 + (d_fftlen%2);
d_lenneg = d_fftlen/2;
assert(d_lenpos + d_lenneg == d_fftlen);
d_buf.resize(d_lenpos);
}
protected:
private:
size_t d_fftlen; // FFT length
size_t d_lenpos; // number of FFT bins with positive frequencies
size_t d_lenneg; // number of FFT bins with negative frequencies
std::vector<T> d_buf; // buffer used for cyclic shift
} ;
} // namespace fft
} // namespace gr
#endif // INCLUDED_FFT_FFT_SHIFT_H
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