Prime95 v30.4/30.5/30.6

[drkirkby]

Oops. Given you say it's completed, there's probably no harm in having the AID printed, as it would be expired now. At least I think that's the case - I would still not print it myself, just in case, but I think you are safe the fact it has completed.

[Viliam Furik]

Originally Posted by RichD

My session time was reset so I was able to connect to CoLab. My worktodo entry was:

PRPDC=194......D8F,1,2,11115983,-1,99,0,3,1,"1267222063"

So I let it run. It finally credited me with the exponent in the worktodo file even though every output line showed the rogue exponent!

I have an unconfirmed feeling that it happens on all exponents, because it doesn't iterate the entire Mersenne number, but only the cofactor, which is smaller by the size of known factors.

The fact, that the factor has 31 bits (rounded up) suggests it's true because 11115983 - 31 = 11115952.

[RichD]

Originally Posted by Viliam Furik

I have an unconfirmed feeling that it happens on all exponents, because it doesn't iterate the entire Mersenne number, but only the cofactor, which is smaller by the size of known factors.

The fact, that the factor has 31 bits (rounded up) suggests it's true because 11115983 - 31 = 11115952.

My next one, before the session expired, appears to be correct. The output line:

[Work thread Jun 13 03:17] Iteration: 5800000 / 6397693 [90.65%], ms/iter:  1.524, ETA: 00:15:10

And the worktodo entry:

PRPDC=5F.....9D,1,2,6397693,-1,99,0,3,5,"1880921743,150224692370214966223"

This one is not completed so the AID is masked.

[Happy5214]

Originally Posted by Viliam Furik

Except for the 2kp+1 form, which holds for any factor of Mp.

Well, of course there's that. I should have said there was no special binary form, beyond a couple of bits (guaranteed by the 2kp+1 form). Recall, a Mersenne number is all 1's in binary.

[Viliam Furik]

Originally Posted by Happy5214

Well, of course there's that. I should have said there was no special binary form, beyond a couple of bits (guaranteed by the 2kp+1 form). Recall, a Mersenne number is all 1's in binary.

Yes, of course. I just wanted to point out the tiny error that made the statement false. Otherwise, I agree.

[ATH]

Weird single exponent FFT issue: I'm doing P+1 in the 4M range in mprime 30.6b4 and at the exponent M4037479 kept failing with the chosen AVX-512 FFT 200K.
Pplus1=N/A,1,2,4037479,-1,2500000,250000000,1,70

It did not work until I added ExtraSafetymargin=0.03 to prime.txt forcing it to use 240K FFT.

But subsequent exponents works fine at AVX-512 FFT 200K, and that exponent M4037479 also works fine with FMA3 FFT 200K (in Prime95 30.6b4).

[Work thread Jun 20 12:38:29] P+1 on M4037479, start=2/7, B1=2500000, B2=TBD
[Work thread Jun 20 12:38:29] Using AVX-512 FFT length 200K, Pass1=640, Pass2=320, clm=1
[Work thread Jun 20 12:42:20] Possible roundoff error (0.44758343), backtracking to last save file.
[Work thread Jun 20 12:42:20] Using AVX-512 FFT length 200K, Pass1=640, Pass2=320, clm=1
[Work thread Jun 20 12:46:12] Possible roundoff error (0.44758343), backtracking to last save file.
[Work thread Jun 20 12:46:12] Using AVX-512 FFT length 200K, Pass1=640, Pass2=320, clm=1
[Work thread Jun 20 12:50:12] Possible roundoff error (0.44758343), backtracking to last save file.

[Prime95]

Originally Posted by ATH

Weird single exponent FFT issue: I'm doing P+1 in the 4M range in mprime 30.6b4 and at the exponent M4037479 kept failing with the chosen AVX-512 FFT 200K.

That happened to me too a week ago. I changed the code (in 30.7) so that if an error occurs it retries with a maximum allowable error of 0.46. I suppose it could still infinite loop if an even worse roundoff error is encountered.

[ATH]

Happened again and only for 200K AVX-512, worked fine on 200K FMA3. I will leave ExtraSafetymargin=0.03 on for now and use 240K AVX-512.

[Work thread Jun 24 22:19:42] P+1 on M4040059, start=2/7, B1=2500000, B2=TBD

[Work thread Jun 24 23:52:22] Possible roundoff error (0.43976434), backtracking to last save file.
[Work thread Jun 24 23:52:22] Using AVX-512 FFT length 200K, Pass1=640, Pass2=320, clm=1
[Work thread Jun 24 23:52:22] M4040059 stage 1 is 70.105240% complete.
[Work thread Jun 24 23:59:19] Possible roundoff error (0.43976434), backtracking to last save file.
[Work thread Jun 24 23:59:19] Using AVX-512 FFT length 200K, Pass1=640, Pass2=320, clm=1
[Work thread Jun 24 23:59:19] M4040059 stage 1 is 70.105240% complete.
[Work thread Jun 25 00:06:16] Possible roundoff error (0.43976434), backtracking to last save file.

[Prime95]

Originally Posted by ATH

Happened again and only for 200K AVX-512

I'll lower the maximum allowable exponent for AVX-512 200K FFT to 4037000. I'll start testing the maximums of other FFT lengths.

[ATH]

Originally Posted by Prime95

I'll lower the maximum allowable exponent for AVX-512 200K FFT to 4037000. I'll start testing the maximums of other FFT lengths.

You need help testing AVX-512 or FMA3 candidates?

It could be hard to find though, since not all exponents above a certain threshold gives the error.
I turned back to AVX-512 200K FFT for a while before I got the 2nd error, and these 7 exponents worked fine at 200K:
M4039429,M4039447,M4039487,M4039537,M4039583,M4039733,M4039843


I guess this could not be an mprime issue? Just in case could someone with a Prime95 (Windows) AVX-512 computer test one of these? No need to finish it unless you want to, just run like 50% of stage1 to check if you get a roundoff error:
Pplus1=N/A,1,2,4037479,-1,2500000,250000000,2,70
Pplus1=N/A,1,2,4040059,-1,2500000,250000000,2,70

[Prime95]

Originally Posted by ATH

You need help testing AVX-512 or FMA3 candidates?

It could be hard to find though, since not all exponents above a certain threshold gives the error.
I turned back to AVX-512 200K FFT for a while before I got the 2nd error, and these 7 exponents worked fine at 200K:
M4039429,M4039447,M4039487,M4039537,M4039583,M4039733,M4039843

I guess this could not be an mprime issue? Just in case could someone with a Prime95 (Windows) AVX-512 computer test one of these?

Sure, help is welcome. A stray roundoff error of 0.43 or 0.44 is not too alarming. Yours was because you weren't that close to the FFT maximum of 4043000. I tested the 16K FFT maximum. I'll test the 12800 FFT maximum of 267,400 next. I'll do this by running P-1 and P+1 to largish bounds using the python worktodo generator (ECM would also be a good test) on 266,000 to 267,400. I'm using Windows and prime95. Linux and mprime would provide the same data.

Other AVX-512 FFT maximum exponents that remain to be tested (turn on roundoff checking):

22469
33423
44307
98407
108700
130200
151300
162400
172600
194300
214800
225600
256500
267400
382900
424300
507400
527800
672200
835300
1001000
1161000
1244000
1324000
1490000
1649000
1730000
1976000
2457000
2616000
2941000
3893000
4843000
5623000
5798000
6022000
6408000
6730000
7219000
7682000
7815000
7985000
8384000
8640000
8907000
9547000
10020000