4.1.3 Memory Allocation

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).