[Octave-bug-tracker] [bug #61129] Improve performance of factor() function

[Kai Torben Ohlhus]

Update of bug #61129 (project octave):

                  Status:         Patch Submitted => Patch Reviewed         
                 Summary: Performance of factor(). Proposed patch attached. =>
Improve performance of factor() function

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Follow-up Comment #17:

Thank you for the important hint @mleitner.  This announcement would indeed be
disappointing in many cases.  See additional tests below.

Final modified reviewed patch (file #52034) for pushing tomorrow.

Large prime with 19 digits 2305843009213693951
https://en.wikipedia.org/wiki/Mersenne_prime#List_of_known_Mersenne_primes

Single large prime:


>> x = [uint64(230584300921369) * 10000 + 3951];

>> tic, factor (x), t1 = toc
ans = 2305843009213693951
t1 = 49.933

>> tic, factor6 (x), t2 = toc
ans = 2305843009213693951
t2 = 11.059

>> t1 / t2
ans = 4.5153


Three large primes:


>> x = uint64 (8191) * 524287 * 2147483647
x = 9222228542614937599

>> tic, factor (x), t1 = toc
ans =

        8191      524287  2147483647

t1 = 103.96

>> tic, factor6 (x), t2 = toc
ans =

        8191      524287  2147483647

t2 = 22.123

>> t1 / t2
ans = 4.6992



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