cfftopt (3p)

Name

cfftopt - compute the length of the closest fast FFT

Synopsis

INTEGER FUNCTION CFFTOPT(LEN)

INTEGER LEN

INTEGER*8 FUNCTION CFFTOPT_64(LEN)

INTEGER*8 LEN




F95 INTERFACE
INTEGER FUNCTION CFFTOPT(LEN)

INTEGER :: LEN

INTEGER(8) FUNCTION CFFTOPT_64(LEN)

INTEGER(8) :: LEN




C INTERFACE
#include <sunperf.h>

int cfftopt(int len);

long cfftopt_64(long len);

Description

Oracle Solaris Studio Performance Library                          cfftopt(3P)



NAME
       cfftopt - compute the length of the closest fast FFT


SYNOPSIS
       INTEGER FUNCTION CFFTOPT(LEN)

       INTEGER LEN

       INTEGER*8 FUNCTION CFFTOPT_64(LEN)

       INTEGER*8 LEN




   F95 INTERFACE
       INTEGER FUNCTION CFFTOPT(LEN)

       INTEGER :: LEN

       INTEGER(8) FUNCTION CFFTOPT_64(LEN)

       INTEGER(8) :: LEN




   C INTERFACE
       #include <sunperf.h>

       int cfftopt(int len);

       long cfftopt_64(long len);



PURPOSE
       cfftopt  computes  the  length  of  the closest fast FFT.  Fast Fourier
       transform algorithms, including those used in Performance Library, work
       best  with vector lengths that are products of small primes.  For exam-
       ple, an FFT of length 32=2**5 will run faster  than  an  FFT  of  prime
       length  31  because  32 is a product of small primes and 31 is not.  If
       your application is such that you can taper or zero pad your vector  to
       a  larger length then this function may help you select a better length
       and run your FFT faster.

       CFFTOPT will return an integer no smaller than  the  input  argument  N
       that  is  the  closest  number  that  is  the  product of small primes.
       CFFTOPT will return 16 for an input of N=16 and return 18=2*3*3 for  an
       input of N=17.

       Note  that  the  length  computed here is not guaranteed to be optimal,
       only to be a product of small primes.  Also,  the  value  returned  may
       change as the underlying FFTs become capable of handling larger primes.
       For example, passing in N=51 today will return  52=2*2*13  rather  than
       51=3*17  because the FFTs in Performance Library do not have fast radix
       17 code.  In the future, radix 17 code may be added and then N=51  will
       return 51.




                                  7 Nov 2015                       cfftopt(3P)