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  1. #include <cstddef>
  2. #include <iostream>
  3. #include <vector>
  4. #include <algorithm>
  5.  
  6. typedef std::size_t index_t;
  7. typedef double element_t;
  8. typedef std::vector<element_t> row_t;
  9. typedef std::vector<row_t> slice_t;
  10. typedef std::vector<slice_t> array_3d_t;
  11.  
  12. // for one dimension
  13. template<class T>
  14. void fftshift_dimension(std::vector<T>& row)
  15. {
  16.   using std::swap;
  17.   const index_t size = row.size();
  18.   if(size <= 1)
  19.     return;
  20.   const index_t halved_size = size / 2;
  21.   //swap the two halves
  22.   for(index_t i = 0, j = size - halved_size ; i < halved_size ; ++i, ++j)
  23.     swap(row[i], row[j]);
  24.   // if the size is odd, rotate the right part
  25.   if(size % 2)
  26.   {
  27.     swap(row[halved_size], row[size - 1]);
  28.     const index_t n = size - 2;
  29.     for(index_t i = halved_size ; i < n ; ++i)
  30.       swap(row[i], row[i + 1]);
  31.   }
  32. }
  33.  
  34. // base case
  35. template<class T>
  36. void fftshift(std::vector<T>& array) {
  37.   fftshift_dimension(array);
  38. }
  39.  
  40. // reduce the problem for a dimension N+1 to a dimension N
  41. template<class T>
  42. void fftshift(std::vector<std::vector<T>>& array) {
  43.   fftshift_dimension(array);
  44.   for(auto& slice : array)
  45.     fftshift(slice);
  46. }
  47.  
  48. // overloads operator<< to print a 3-dimensional array
  49. std::ostream& operator<<(std::ostream& output, const array_3d_t& input) {
  50.   const index_t width = input.size();
  51.   for(index_t i = 0; i < width ; i++)
  52.   {
  53.     const index_t height = input[i].size();
  54.     for(index_t j = 0; j < height ; j++)
  55.     {
  56.       const index_t depth = input[i][j].size();
  57.       for(index_t k = 0; k < depth; k++)
  58.         output << input[i][j][k] << ' ';
  59.       output << '\n';
  60.     }
  61.     output << '\n';
  62.   }
  63.   return output;
  64. }
  65.  
  66. int main()
  67. {
  68.   constexpr index_t width = 3;
  69.   constexpr index_t height = 4;
  70.   constexpr index_t depth = 5;
  71.  
  72.   array_3d_t input(width, slice_t(height, row_t(depth)));
  73.  
  74.   // initialization
  75.   for(index_t i = 0 ; i < width ; ++i)
  76.     for(index_t j = 0 ; j < height ; ++j)
  77.       for(index_t k = 0 ; k < depth ; ++k)
  78.         input[i][j][k] = i + j + k;
  79.   std::cout << input;
  80.  
  81.   // in place fftshift
  82.   fftshift(input);
  83.  
  84.   std::cout << "and then" << '\n' << input;
  85. }
  86.  
Success #stdin #stdout 0s 3460KB
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stdin
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Standard input is empty
stdout
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0 1 2 3 4 
1 2 3 4 5 
2 3 4 5 6 
3 4 5 6 7 

1 2 3 4 5 
2 3 4 5 6 
3 4 5 6 7 
4 5 6 7 8 

2 3 4 5 6 
3 4 5 6 7 
4 5 6 7 8 
5 6 7 8 9 

and then
7 8 4 5 6 
8 9 5 6 7 
5 6 2 3 4 
6 7 3 4 5 

5 6 2 3 4 
6 7 3 4 5 
3 4 0 1 2 
4 5 1 2 3 

6 7 3 4 5 
7 8 4 5 6 
4 5 1 2 3 
5 6 2 3 4
https://ideone.com/o1Vk6r
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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