FFT991/admissible_fft.C
/*
* Determines whether a given number of points N is allowed by the
* Fast Fourier Transform algorithm, i.e. if
*
* N = 2^p 3^q 5^r and N >= 4, p>=1
*
*/
/*
* Copyright (c) 1999-2001 Eric Gourgoulhon
*
* This file is part of LORENE.
*
* LORENE 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 2 of the License, or
* (at your option) any later version.
*
* LORENE 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 LORENE; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
char admissible_fft_C[] = "$Header: /cvsroot/Lorene/C++/Source/Non_class_members/Coef/FFT991/admissible_fft.C,v 1.2 2014/10/15 12:48:19 j_novak Exp $" ;
/*
* $Id: admissible_fft.C,v 1.2 2014/10/15 12:48:19 j_novak Exp $
* $Log: admissible_fft.C,v $
* Revision 1.2 2014/10/15 12:48:19 j_novak
* Corrected namespace declaration.
*
* Revision 1.1 2004/12/21 17:06:01 j_novak
* Added all files for using fftw3.
*
* Revision 1.1.1.1 2001/11/20 15:19:29 e_gourgoulhon
* LORENE
*
* Revision 1.1 1999/11/24 16:06:52 eric
* Initial revision
*
*
* $Header: /cvsroot/Lorene/C++/Source/Non_class_members/Coef/FFT991/admissible_fft.C,v 1.2 2014/10/15 12:48:19 j_novak Exp $
*
*/
namespace Lorene {
bool admissible_fft(int n) {
if (n < 4) {
return false ;
}
// Division by 2
//--------------
int reste = n % 2 ;
if (reste != 0) {
return false ;
}
int k = n/2 ;
while ( k % 2 == 0 ) {
k = k / 2 ;
}
if (k == 1) return true ; // n = 2^p
// Division by 3
//--------------
while ( k % 3 == 0 ) {
k = k / 3 ;
}
if (k == 1) return true ; // n = 2^p * 3^q
// Division by 5
//--------------
while ( k % 5 == 0 ) {
k = k / 5 ;
}
if (k == 1) return true ; // n = 2^p * 3^q * 5^r
return false ;
}
}
Lorene
Lorene prototypes.
Definition app_hor.h:64