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256bit inputs are small, and YAFU will run the quadratic sieve to factor them. This method is faster for inputs below about 100 decimal digits, but the time to factor scales more steeply than the Number Field Sieve (NFS).
384 bits is well above that 100 digits, so YAFU is running NFS.
What you see on screen is the output of the first phase of NFS algorithm polynomial selection. That phase will run for roughly 5% of the total factorization time. Sieving takes 8085% of the total time, and the linear algebra takes 1015% at the end.
A 384bit input on a desktop quadcore should take a couple hours to factor. Difficulty doubles every 5 decimal digits or so, so a 512bit number will take 510 days (depending on the speed of your hardware).
