cannam@95: Next: Wisdom, cannam@95: Previous: Guru Interface, cannam@95: Up: FFTW Reference cannam@95:
cannam@95: Normally, one executes a plan for the arrays with which the plan was
cannam@95: created, by calling fftw_execute(plan) as described in Using Plans.
cannam@95: However, it is possible for sophisticated users to apply a given plan
cannam@95: to a different array using the “new-array execute” functions
cannam@95: detailed below, provided that the following conditions are met:
cannam@95:
cannam@95:
ii-ri and io-ro, are the same as they were for
cannam@95: the input and output arrays when the plan was created. (This
cannam@95: condition is automatically satisfied for interleaved arrays.)
cannam@95:
cannam@95: FFTW_UNALIGNED flag.
cannam@95: Here, the alignment is a platform-dependent quantity (for example, it is
cannam@95: the address modulo 16 if SSE SIMD instructions are used, but the address
cannam@95: modulo 4 for non-SIMD single-precision FFTW on the same machine). In
cannam@95: general, only arrays allocated with fftw_malloc are guaranteed to
cannam@95: be equally aligned (see SIMD alignment and fftw_malloc).
cannam@95:
cannam@95: The alignment issue is especially critical, because if you don't use
cannam@95: fftw_malloc then you may have little control over the alignment
cannam@95: of arrays in memory. For example, neither the C++ new function
cannam@95: nor the Fortran allocate statement provide strong enough
cannam@95: guarantees about data alignment. If you don't use fftw_malloc,
cannam@95: therefore, you probably have to use FFTW_UNALIGNED (which
cannam@95: disables most SIMD support). If possible, it is probably better for
cannam@95: you to simply create multiple plans (creating a new plan is quick once
cannam@95: one exists for a given size), or better yet re-use the same array for
cannam@95: your transforms.
cannam@95:
cannam@95:
If you are tempted to use the new-array execute interface because you cannam@95: want to transform a known bunch of arrays of the same size, you should cannam@95: probably go use the advanced interface instead (see Advanced Interface)). cannam@95: cannam@95:
The new-array execute functions are: cannam@95: cannam@95:
void fftw_execute_dft( cannam@95: const fftw_plan p, cannam@95: fftw_complex *in, fftw_complex *out); cannam@95: cannam@95: void fftw_execute_split_dft( cannam@95: const fftw_plan p, cannam@95: double *ri, double *ii, double *ro, double *io); cannam@95: cannam@95: void fftw_execute_dft_r2c( cannam@95: const fftw_plan p, cannam@95: double *in, fftw_complex *out); cannam@95: cannam@95: void fftw_execute_split_dft_r2c( cannam@95: const fftw_plan p, cannam@95: double *in, double *ro, double *io); cannam@95: cannam@95: void fftw_execute_dft_c2r( cannam@95: const fftw_plan p, cannam@95: fftw_complex *in, double *out); cannam@95: cannam@95: void fftw_execute_split_dft_c2r( cannam@95: const fftw_plan p, cannam@95: double *ri, double *ii, double *out); cannam@95: cannam@95: void fftw_execute_r2r( cannam@95: const fftw_plan p, cannam@95: double *in, double *out); cannam@95:cannam@95:
cannam@95: These execute the plan to compute the corresponding transform on
cannam@95: the input/output arrays specified by the subsequent arguments. The
cannam@95: input/output array arguments have the same meanings as the ones passed
cannam@95: to the guru planner routines in the preceding sections. The plan
cannam@95: is not modified, and these routines can be called as many times as
cannam@95: desired, or intermixed with calls to the ordinary fftw_execute.
cannam@95:
cannam@95:
The plan must have been created for the transform type
cannam@95: corresponding to the execute function, e.g. it must be a complex-DFT
cannam@95: plan for fftw_execute_dft. Any of the planner routines for that
cannam@95: transform type, from the basic to the guru interface, could have been
cannam@95: used to create the plan, however.
cannam@95:
cannam@95:
cannam@95:
cannam@95: