CZT: Do Bluestein algorithm perform backward transformation?
It is easy to calculate IDFT using DFT, by applying the property:
$$\operatorname{IDFT}(x) = \frac{1}{N}\big(\operatorname{DFT}(x^*)\big)^*,\tag{1}$$
where $^*$ denotes elementwise complex conjugation. You can find this equation in a more verbose form in Eq. 13-55 of Richard G. Lyons &quot;Understanding Digital Signal Processing&quot; 3rd edition.
Probably this was used along with conjugation properties of the exponential.