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Old 2016-07-17, 14:36   #1
ET_'s Avatar
Aug 2002
Team Italia

4,813 Posts
Default ecm with Fermat numbers

Question: with regard to both mprime and gmp-ecm, is it faster running the Fermat number "as-is", or divided by its known factors?

IIRC, mprime was faster using the standard notation and providing the known factors either on the worktodo.txt line or on the lowp.txt file, while gmp-ecn was faster as the number to test grew smaller.

Is it still correct?


Last fiddled with by ET_ on 2016-07-17 at 14:37
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Old 2016-08-02, 19:40   #2
GP2's Avatar
Sep 2003

50358 Posts

As an experiment, I decided to run mprime twice on the same machine, once with the known factors and once without.

This was using the latest version, 28.9

In other words:


Stage 1:
The two versions ran absolutely identically. The second version was maybe 0.1% faster.

Stage 2:
The first version completed stage 2 in 42% of the time that stage 1 took.

The second version "discovered" a composite factor after stage 1 and stopped without doing stage 2.

PS, when I run ECM exponents I always add:

to prime.txt for convenience, to avoid excessively rapid output for small exponents. See undoc.txt for explanations.

You can also add

if you like.

Last fiddled with by GP2 on 2016-08-02 at 19:46
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