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/*
* Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
* Copyright (C) 2008 - INRIA - Allan SIMON
*
* This file must be used under the terms of the CeCILL.
* This source file is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
* are also available at
* http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt
*
*/
#include "fft_internal.h"
/*
** radix 4 iteration subroutine
*/
/* this function do in one turn the same computation that do radix 2 in two turns */
void r4tx( int nthpo, doubleComplex* c0, doubleComplex* c1, doubleComplex* c2, doubleComplex* c3)
{
int kk;
doubleComplex temp1 , temp2 , temp3 , temp4 ;
for(kk=0;kk<nthpo;kk+=4)
{
/* real and imag parts alternate */
/* this first step is strictly equivalent than calling radix 2
except that radix would have needed 2 turns to compute what radix4 do in one */
temp1 = zadds ( c0[kk] , c2[kk] ) ;
temp2 = zdiffs( c0[kk] , c2[kk] ) ;
temp3 = zadds ( c1[kk] , c3[kk] ) ;
temp4 = zdiffs( c1[kk] , c3[kk] ) ;
/* strictly equivalent than calling radix2 with the temporary vector , but here also , radix4 do it in one turn
instead of two */
c0[kk] = zadds ( temp1 , temp3 );
c1[kk] = zdiffs( temp1 , temp3 );
c2[kk] = DoubleComplex ( zreals ( temp2 ) - zimags( temp4 ) , zimags ( temp2 ) + zreals( temp4 ) );
c3[kk] = DoubleComplex ( zreals ( temp2 ) + zimags( temp4 ) , zimags ( temp2 ) - zreals( temp4 ) );
}
}
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