nts on the input/output arrays (i.e. no
SIMD may be used).  This flag is normally <em>not necessary</em>, since
the planner automatically detects misaligned arrays.  The only use for
this flag is if you want to use the new-array execute interface to
execute a given plan on a different array that may not be aligned like
the original.  (Using <code>fftw_malloc</code> makes this flag unnecessary
even then.  You can also use <code>fftw_alignment_of</code> to detect
whether two arrays are equivalently aligned.)
