fftshift.h

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#ifndef __stir_numerics_fftshift_H__
#define __stir_numerics_fftshift_H__
/*
    Copyright (C) 2025, University College London
    This file is part of STIR.

    SPDX-License-Identifier: Apache-2.0

    See STIR/LICENSE.txt for details
*/
#include "stir/Array.h"
#include <complex>
#include <utility> // for std::swap

START_NAMESPACE_STIR

template <typename T>
inline void
fftshift(Array<1, T>& a, int size)
{
  for (int i = 0; i < size / 2; ++i)
    std::swap(a[i], a[size / 2 + i]);
}

template <typename T>
inline void
fftshift(Array<2, std::complex<T>>& a, int size)
{
  // swap left/right halves across all rows
  for (int i = 0; i < size; ++i)
    for (int j = 0; j < size / 2; ++j)
      std::swap(a[i][j], a[i][size / 2 + j]);

  // swap top/bottom halves across all columns
  for (int i = 0; i < size; ++i)
    for (int j = 0; j < size / 2; ++j)
      std::swap(a[j][i], a[size / 2 + j][i]);
}

END_NAMESPACE_STIR
#endif