FT of size <code>n</code>, stored as a sequence of <code>n</code> real
numbers (<code>double</code>) in the format:
</p>
<p align=center>
r<sub>0</sub>, r<sub>1</sub>, r<sub>2</sub>, ..., r<sub>n/2</sub>, i<sub>(n+1)/2-1</sub>, ..., i<sub>2</sub>, i<sub>1</sub>
</p>

<p>Here,
r<sub>k</sub>
is the real part of the <em>k</em>th output, and
i<sub>k</sub>
is the imaginary part.  (Division by 2 is rounded down.) For a
halfcomplex array <code>hc[n]</code>, the <em>k</em>th component thus has its
real part in <cod