fftw3: 64-bit Guru Interface
4.5.6 64-bit Guru Interface
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When compiled in 64-bit mode on a 64-bit architecture (where addresses
are 64 bits wide), FFTW uses 64-bit quantities internally for all
transform sizes, strides, and so on--you don't have to do anything
special to exploit this. However, in the ordinary FFTW interfaces, you
specify the transform size by an 'int' quantity, which is normally only
32 bits wide. This means that, even though FFTW is using 64-bit sizes
internally, you cannot specify a single transform dimension larger than
2^31-1 numbers.
We expect that few users will require transforms larger than this,
but, for those who do, we provide a 64-bit version of the guru interface
in which all sizes are specified as integers of type 'ptrdiff_t' instead
of 'int'. ('ptrdiff_t' is a signed integer type defined by the C
standard to be wide enough to represent address differences, and thus
must be at least 64 bits wide on a 64-bit machine.) We stress that
there is _no performance advantage_ to using this interface--the same
internal FFTW code is employed regardless--and it is only necessary if
you want to specify very large transform sizes.
In particular, the 64-bit guru interface is a set of planner routines
that are exactly the same as the guru planner routines, except that they
are named with 'guru64' instead of 'guru' and they take arguments of
type 'fftw_iodim64' instead of 'fftw_iodim'. For example, instead of
'fftw_plan_guru_dft', we have 'fftw_plan_guru64_dft'.
fftw_plan fftw_plan_guru64_dft(
int rank, const fftw_iodim64 *dims,
int howmany_rank, const fftw_iodim64 *howmany_dims,
fftw_complex *in, fftw_complex *out,
int sign, unsigned flags);
The 'fftw_iodim64' type is similar to 'fftw_iodim', with the same
interpretation, except that it uses type 'ptrdiff_t' instead of type
'int'.
typedef struct {
ptrdiff_t n;
ptrdiff_t is;
ptrdiff_t os;
} fftw_iodim64;
Every other 'fftw_plan_guru' function also has a 'fftw_plan_guru64'
equivalent, but we do not repeat their documentation here since they are
identical to the 32-bit versions except as noted above.
Info Catalog
fftw3: Guru Real-to-real Transforms
fftw3: Guru Interface