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/**
* Copyright 1981-2007 ECMWF
*
* Licensed under the GNU Lesser General Public License which
* incorporates the terms and conditions of version 3 of the GNU
* General Public License.
* See LICENSE and gpl-3.0.txt for details.
*/
#include "fortint.h"
#ifndef CRAY
#ifdef FORTRAN_NO_UNDERSCORE
#define FFTCHK fftchk
#else
#define FFTCHK fftchk_
#endif
#endif
#ifdef REAL_8
fortint FFTCHK(fortint * trunc, double * longinc)
#else
fortint FFTCHK(fortint * trunc, float * longinc)
#endif
{
/* Checks if the given truncation and longitude increment can be handled
by the FFT routine used in the interpolation scheme.
Returns 1 if it can, otherwise 0.
For calculation purposes, the number of longitude points has to be
greater than 2*(output truncation) to ensure that the fourier
transform is exact. For more information see page 10 in:
E.C.M.W.F. Research Department technical memorandum no. 56
"The forecast and analysis post-processing package"
May 1982. J.Haseler.
*/
long nlonpts = (long) ( (360.0/(*longinc)) + 0.5 );
/* Set number of longitude points > 2*truncation */
while( nlonpts < 2*(*trunc) ) nlonpts *= 2;
/* Look for allowed factors: 8, 6, 5, 4 ,3 , 2 */
/* Check 6 first */
while( nlonpts%6 == 0 ) nlonpts /= 6;
/* 8 only allowed once as a factor */
if( nlonpts%8 == 0 ) nlonpts /= 8;
while( nlonpts%5 == 0 ) nlonpts /= 5;
while( nlonpts%4 == 0 ) nlonpts /= 4;
while( nlonpts%3 == 0 ) nlonpts /= 3;
while( nlonpts%2 == 0 ) nlonpts /= 2;
if( nlonpts != 1) return (fortint) 0;
return (fortint) 1;
}
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