I hadn't noticed this until a day or two ago. I moved a worker from a slower computer and found the following:

[Worker #1 May 8 18:04] Resuming PRP test of 24737*2^18572071+1 using zero-padded FFT length 2048K, 2 threads
[Worker #1 May 8 18:04] Iteration: 1382378 / 18572085 [7.44%].
[Worker #2 May 8 18:04] Resuming PRP test of 21181*2^17999900+1 using all-complex FFT length 1536K, 2 threads
[Worker #2 May 8 18:04] Iteration: 15725838 / 17999914 [87.36%].


What is the difference between a zero-padded FFT and one that uses all complex FFT length? I'm assuming the new FFT length is required (and becomes larger as we approach larger n values).