Macro FFT_REV_LOGS

#define FFT_REV_LOGS 14

Compile-time bit-reversal swap lists for every length up to FFT_CONST_N: for n = 2^L, the pairs (i, rev i) with i < rev i, in increasing i, at p[2 * off[L] ..]. Swapping from a list skips the per-element index walk and the unpredictable i < j branch of the loop below.