[tor-bugs] #28142 [Core Tor/Tor]: Merge original WTF-PAD branch

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#28142: Merge original WTF-PAD branch
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 Reporter:  asn                                  |          Owner:
                                                 |  mikeperry
     Type:  enhancement                          |         Status:
                                                 |  needs_review
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.4.0.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  wtf-pad, tor-relay, tor-cell,        |  Actual Points:
  padding                                        |
Parent ID:                                       |         Points:
 Reviewer:  asn                                  |        Sponsor:
                                                 |  Sponsor2
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Comment (by asn):

 The last few days I've been focusing on using Riastradh's better
 probability distribution formulas as part of circuitpadding. Current work
 can be found in https://github.com/torproject/tor/pull/533.

 Next steps in this area:
 - Fix the remaining compiler warnings.
 - Figure out if we want to keep the stochastic tests or not. Need to
 understand more about their failure rates, and also they are quite slow.
 Maybe I can put them into the slow test category which AFAIK is not run by
 the CI. We still get to run the numerical tests.
 - Address various XXXs (e.g. geometric distr needs to conform to the API
 as well).
 - Do further documentation.
 - Ensure that the API consumer `circpad_distribution_sample()` works well
 in terms of using the prob distributions correctly.
 - The new files were ported to Tor quite hastily. Ensure that they are
 proper wrt header file etc. Also fix the copyrights etc.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28142#comment:9>
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