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Old 2019-04-20, 14:01   #1
pepi37
 
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Dec 2011
After milion nines:)

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Default GFN 17 ( exponent 131072)

Since I got shiny new GPU, I was playing at home with GFN ( 131072) and found one big problem. I download from http://www.underbakke.com/AthGFNsv/ latest version (64 bit) run it and got initial sieve file. Sieve was done up to 1P since from that point I can continue with sieveless GPU program . So far so good , but no.
For curiosity I take few candidates left and run it under Prime95 and found they all have small factor! So I retested again with PFGW and found again that factor was found with Prime95 was correct. So latest version of Underbakke program has serious bug. So I do step back and download 32 bit much older version of same program and found that on same sieve depth I have nearly 30% less candidate!


So question is : does any of you know any other software to generate initial sieve file. After 1P of sieve depth it is easy :)


Thanks for reply
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Old 2019-04-20, 16:53   #2
mackerel
 
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I also ran into that bug when doing GFN13/14 in the past, and it seemed like it was a known problem that's been around for a long time.

The recommendation I got was to start the sieve with 32 bit version, let it run for some time, then switch to the 64 bit version. Apparently the 64 bit version had some problems at low p, although I don't know exactly at what point it was safe to switch over.
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Old 2019-04-20, 16:58   #3
pepi37
 
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Quote:
Originally Posted by mackerel View Post
I also ran into that bug when doing GFN13/14 in the past, and it seemed like it was a known problem that's been around for a long time.

The recommendation I got was to start the sieve with 32 bit version, let it run for some time, then switch to the 64 bit version. Apparently the 64 bit version had some problems at low p, although I don't know exactly at what point it was safe to switch over.



So my approach was OK. I will finish on CPU up to 1P on 32 bit version of program and then continue on GPU :)
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Old 2019-04-22, 08:30   #4
DukeBG
 
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Just so that you wouldn't repeat work done by others, you should know that GFN-17 (along with others) is something that is ran on PrimeGrid. PrimeGrid's GFN-17 sieve is done up to 175000P.
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Old 2019-04-22, 08:38   #5
pepi37
 
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Quote:
Originally Posted by DukeBG View Post
Just so that you wouldn't repeat work done by others, you should know that GFN-17 (along with others) is something that is ran on PrimeGrid. PrimeGrid's GFN-17 sieve is done up to 175000P.
I know that, and even I found prime I will not interfere PG work :)
After many years of learning , it come time when you go further and you stop be depend on others. Be yourself.
I already told to PG admins what is my intention and got his response. So dont worry
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