PSIQS Change Log
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Version 01.00 (2016-01-15):
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* Initial release
Version 01.01 (2016-01-15):
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* Suppress exception when then executable jar is terminated with Ctrl-C
* Added more parametric class SquFoF63_02
Version 01.02 (2016-01-17):
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* Added log4j xml-configuration that allows logging into a file, too
* Extended class SquFoF63_02 to support hand-selected multiplier lists
Version 02.00 (2017-01-31):
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The main goal in version 02.00 was to improve SIQS in terms of speed, memory requirements, structure and readability.
SIQS and PSIQS have become significantly faster than in version 01, about factor 3 or even more for large factor arguments (300 bit and more).
Let's compare some average timings of PSIQS(6 threads) on my notebook:
Version 01: ~3s @ 200bit, ~2min @ 250 bit, ~90min @ 300 bit
Version 02: ~2.5s @ 200bit, ~1min @ 250 bit, ~30min @ 300 bit
This was mostly achieved due to the following changes:
* Now primes are permitted that exceed the sieve array size (it was a major performance bug in version 01 not to do so)
* The primes q_l forming the a-parameter are now filtered out before sieving.
* The sieve has been rolled out for large primes.
* Polynomial switching has become much faster. Exchanging the sub-indices of the Bainv2[][] from Bainv2[p][v] to Bainv2[v][p] had a large impact here.
* Trial division (aka resieving) has been sped up by about 20%, too.
* I managed to interface Dario Alpern's Block-Lanczos solver. (a big thanks to Dario for the permission to use it!)
* The computation of the A and sqrt(Q)-values of the final congruence A^2 == Q (mod kN) (where Q is a square) is now done (mod N).
A second important point was to reduce the memory consumption.
(P)SIQS stores all partials in memory, which will become very expensive for large factor arguments.
The memory demands have been reduced a lot by the following measures:
* Store large factors as long, not as BigInteger.
* Introduce particular subclasses for partials with 1 and 2 factors; in Java this is much cheaper than storing an array of large factors.
* Some further overhead in the data structures used to store partials was removed.
While PSIQS 01 with 12 GB RAM failed to factor 340 bit numbers because of memory problems, with PSIQS 02 such numbers require only about 3.4 GB RAM.
I estimate that with 12 GB RAM, PSIQS 02 should be capable to factor 380 bit numbers. But for such large numbers, NFS should be used anyway.
Structure and readability have been improved in many parts of PSIQS.
Some of the changes include
* Basic QS and MPQS have been dropped. They are documented in version 01, which will be available further-on.
* Many lazy initializations have been replaced by more direct, mandatory initializations.
* The Poly interface and it's subclasses have been removed completely.
* The computation of ainv[], Bainv2[][] and first x-arrays is now done in a single loop.
* Many more small changes.
* Many updated comments.
A second focus was the improvement of some BigInteger argument functions like SqrtInt, SqrtExact, Root and PurePowerTest,
following several very helpful comments from Graeme Willoughby (big thanks, Graeme!).
* SqrtInt has been improved by about 20% by using the full mantissa precision of Math.sqrt() to construct the initial guess BigInteger.
* SqrtExact was slightly improved replacing the first modulus (by a power of 2) with a test of the 001 bit pattern.
* The computation of n.th root of BigIntegers has become much faster (like factor 10) due to a new Heron-style implementation.
* The PurePowerTest has a much better implementation now, too.
Have a look at the comments in the source files, all changes have been explained in detail there.
Last not least I added new implementations of the following algorithms:
* Segmented sieves (both single and double block) following Wambach and Wettig. To my disappointment, in Java these are just slower than monolithic sieves.
The reason for this seems to be that the JVM running as the top-level task absorbs any caching effects. All we get is the additional bookkeeping costs.
* Sieving with powers of small primes. This approach gives a small performance gain for small and medium-size factor arguments.
But for N >= 260 bit or so the effect vanishes. Probably the small number of sieved powers does not justify the overhead introduced by it.
* Brent's improvement of the PollardRho method.
Version 02.01 (2017-02-05):
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* In collaboration with Graeme Willoughby, the test for pure powers has been sped up by another factor around 10
--> in total the speedup since release 01 was about factor 200 !
* Thread-handling in PSIQS has been improved for small N. The parallel version is stable for N>56 bit now.
* Much faster ainvp computation, exploiting that (1/a) mod p = (1/(a%p) mod p