cffts(3P) Sun Performance Library cffts(3P)NAMEcffts - initialize the trigonometric weight and factor tables or com‐
pute the inverse Fast Fourier Transform of a complex sequence as fol‐
lows.
SYNOPSIS
SUBROUTINE CFFTS(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER IOPT, N, IFAC(*), LWORK, IERR
COMPLEX X(*)
REAL SCALE, Y(*), TRIGS(*), WORK(*)
SUBROUTINE CFFTS_64(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER*8 IOPT, N, IFAC(*), LWORK, IERR
REAL SCALE, Y(*), TRIGS(*), WORK(*)
COMPLEX X(*)
F95 INTERFACE
SUBROUTINE FFT(IOPT, N, [SCALE], X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER*4, INTENT(IN) :: IOPT, N
INTEGER*4, INTENT(IN), OPTIONAL :: LWORK
REAL, INTENT(IN), OPTIONAL :: SCALE
COMPLEX, INTENT(IN), DIMENSION(:) :: X
REAL, INTENT(OUT), DIMENSION(:) :: Y
REAL, INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER*4, INTENT(INOUT), DIMENSION(:) :: IFAC
REAL, INTENT(OUT), DIMENSION(:) :: WORK
INTEGER*4, INTENT(OUT) :: IERR
SUBROUTINE FFT_64(IOPT, N, [SCALE], X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER(8), INTENT(IN) :: IOPT, N
INTEGER(8), INTENT(IN), OPTIONAL :: LWORK
REAL, INTENT(IN), OPTIONAL :: SCALE
COMPLEX, INTENT(IN), DIMENSION(:) :: X
REAL, INTENT(OUT), DIMENSION(:) :: Y
REAL, INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER(8), INTENT(INOUT), DIMENSION(:) :: IFAC
REAL, INTENT(OUT), DIMENSION(:) :: WORK
INTEGER(8), INTENT(OUT) :: IERR
C INTERFACE
#include <sunperf.h>
void cffts_ (int *iopt, int *n, float *scale, complex *x, float *y,
float *trigs, int *ifac, float *work, int *lwork, int *ierr);
void cffts_64_ (long *iopt, long *n, float *scale, complex *x, float
*y, float *trigs, long *ifac, float *work, long *lwork, long
*ierr);
PURPOSEcffts initializes the trigonometric weight and factor tables or com‐
putes the inverse Fast Fourier Transform of a complex sequence as fol‐
lows:
N-1
Y(k) = scale * SUM W*X(j)
j=0
where
k ranges from 0 to N-1
i = sqrt(-1)
isign = 1 for inverse transform or -1 for forward transform
W = exp(isign*i*j*k*2*pi/N)
In complex-to-real transform of length N, the (N/2+1) complex input
data points stored are the positive-frequency half of the spectrum of
the Discrete Fourier Transform. The other half can be obtained through
complex conjugation and therefore is not stored. Furthermore, due to
symmetries the imaginary of the component of X(0) and X(N/2) (if N is
even in the latter) is assumed to be zero and is not referenced.
ARGUMENTS
IOPT (input)
Integer specifying the operation to be performed:
IOPT = 0 computes the trigonometric weight table and factor
table
IOPT = 1 computes inverse FFT
N (input)
Integer specifying length of the input sequence X. N is most
efficient when it is a product of small primes. N >= 0.
Unchanged on exit.
SCALE (input)
Real scalar by which transform results are scaled. Unchanged
on exit. SCALE is defaulted to 1.0 for F95 INTERFACE.
X (input) On entry, X is a complex array whose first (N/2+1) elements
are the input sequence to be transformed.
Y (output)
Real array of dimension at least N that contains the trans‐
form results. X and Y may be the same array starting at the
same memory location. Otherwise, it is assumed that there is
no overlap between X and Y in memory.
TRIGS (input/output)
Real array of length 2*N that contains the trigonometric
weights. The weights are computed when the routine is called
with IOPT = 0 and they are used in subsequent calls when IOPT
= 1. Unchanged on exit.
IFAC (input/output)
Integer array of dimension at least 128 that contains the
factors of N. The factors are computed when the routine is
called with IOPT = 0 and they are used in subsequent calls
where IOPT = 1. Unchanged on exit.
WORK (workspace)
Real array of dimension at least N. The user can also choose
to have the routine allocate its own workspace (see LWORK).
LWORK (input)
Integer specifying workspace size. If LWORK = 0, the routine
will allocate its own workspace.
IERR (output)
On exit, integer IERR has one of the following values:
0 = normal return
-1 = IOPT is not 0 or 1
-2 = N < 0
-3 = (LWORK is not 0) and (LWORK is less than N)
-4 = memory allocation for workspace failed
SEE ALSO
fft
6 Mar 2009 cffts(3P)
