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void *fftw_malloc(size_t n); void fftw_free(void *p);

These are functions that behave identically to `malloc`

and
`free`

, except that they guarantee that the returned pointer obeys
any special alignment restrictions imposed by any algorithm in FFTW
(e.g. for SIMD acceleration). See SIMD alignment and fftw_malloc.

Data allocated by `fftw_malloc`

*must* be deallocated by
`fftw_free`

and not by the ordinary `free`

.

These routines simply call through to your operating system’s
`malloc`

or, if necessary, its aligned equivalent
(e.g. `memalign`

), so you normally need not worry about any
significant time or space overhead. You are *not required* to use
them to allocate your data, but we strongly recommend it.

Note: in C++, just as with ordinary `malloc`

, you must typecast
the output of `fftw_malloc`

to whatever pointer type you are
allocating.

We also provide the following two convenience functions to allocate
real and complex arrays with `n`

elements, which are equivalent
to `(double *) fftw_malloc(sizeof(double) * n)`

and
`(fftw_complex *) fftw_malloc(sizeof(fftw_complex) * n)`

,
respectively:

double *fftw_alloc_real(size_t n); fftw_complex *fftw_alloc_complex(size_t n);

The equivalent functions in other precisions allocate arrays of `n`

elements in that precision. e.g. `fftwf_alloc_real(n)`

is
equivalent to `(float *) fftwf_malloc(sizeof(float) * n)`

.