Consider the case of calculating an FFT of a not-quite-1-periodic function $$ t\to f(t) , t \in [0,1] , f(0) \neq f(1) $$ by transforming it into a periodic function :
$$f \to \hat f = f(t) - g(t) = f(t) - t\cdot (f(1)-f(0))$$
we can verify that $$\hat f(0) = f(0)\\\hat f(1) = f(1) - 1\cdot (f(1)-f(0)) = f(0)$$
This removes the step discontinuity at the edge and gives us (assuming f already continuous on the interior of [0,1]) a continuous 1-periodic function.
So consider the alternative forward-procedure
- calculate and store $q = f(1)-f(0)$
- calculate $\hat f(t) = f(t)-qt$
- calculate and store $\hat F = \mathcal{F}(\hat f)$
And corresponding inverse procedure:
- retrieve $\hat F$ and calculate $\hat f = \mathcal{F}^{-1}(\hat F)$
- retrieve $q$ and calculate $f(t) = \hat f(t)+qt$
Does this procedure have any name?