On Wednesday 11 September 2002 13:43, Steve Harris wrote: > I don't think the TF limits were ever lowered;
I haven't checked the source from the latest version but the TF limits should surely be linked in some way to the LL/DC FFT run length crossovers. Many of these _have_ been lowered. Slightly, and especially for P4 systems. > it seems they may have been > raised, as I have gotten several 8.3M DC exponents which first had to be > factored from 63 to 64 and THEN the P-1. Yeah, I've had a number of these, too. I would have thought that, since (ignoring runs with errors - which is a reasonable first approximation) factoring before DC saves only one LL test, whereas factoring before first LL test saves two. So trial factoring (TF) depth for DC assignments should be one bit less than for LL assignments - ignoring efficiency changes due to hardware (word length) constraints, the last bit takes half the total TF time. > It occurred to me that it might be > more efficient to do it the other way around, but factoring from 63 to 64 > goes relative quickly. If it were a question of factoring from 65 to 66 > versus P-1 first, then I think the P-1 wins easily. Again I haven't checked against the new code - TF on P4s is supposed to have been speeded up considerably - but it used to be the case that, assuming trial factoring runs at the same speed irrespective of depth (which is again a reasonable assumption since most TF through 2^64 is completed) it was most effective on a PIII or Athlon to run TF through to N-1, then P-1, then the last "bit" of TF. On P4s the best policy was to run P-1 after TF to N-2 bits. I guess the new P4 TF code will have brought it all into line. Regards Brian Beesley _________________________________________________________________________ Unsubscribe & list info -- http://www.ndatech.com/mersenne/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
