DCexchange - FFTW@wiki

/**
* @brief origin shift (top-left <-> center)
* @author maeda
* @date 2008/09/10
*/
#include "DCexchange.h"
 
/**
* in-place DC exchange for 2dimensional data (top-left <-> center)
* this function works both odd/even size data
* @param data fft data
* @param cols column size of the data ( sometimes the size of x )
* @param rows row size of the data ( sometimes the size of y )
* @return true if succeed
*/
int maDCexchange2D( fftw_complex *data, int cols, int rows )
{
	int i,j;
	int p1,p2;    // point position
	int c2,r2;    // temporary for cols/2,rows/2
	double re,im; // temporary
 
	if( data==NULL )       return false;
	if( rows<0 || cols<0 ) return false;
 
	c2 = cols/2;
	r2 = rows/2;
 
	for( j=0; j<r2; j++ ){
		for( i=0; i<cols; i++ ){
			// exchange p1( i, j ) <-> p2( (cols/2+i)%cols, rows/2+j )
			p1 = j*cols + i;
			p2 = (r2+j)*cols + (c2+i)%cols;
			re = data[p1][0];
			im = data[p1][1];
			data[p1][0] = data[p2][0];
			data[p1][1] = data[p2][1];
			data[p2][0] = re;
			data[p2][1] = im;
		}
	}
 
	return true;
}