[tbb-bugs] #18631 [Tor Browser]: Rewritten #1517 patch for TBB/ESR45

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#18631: Rewritten #1517 patch for TBB/ESR45
-----------------------------------+------------------------------
 Reporter:  arthuredelstein        |          Owner:  tbb-team
     Type:  defect                 |         Status:  needs_review
 Priority:  Medium                 |      Milestone:
Component:  Tor Browser            |        Version:
 Severity:  Normal                 |     Resolution:
 Keywords:  TorBrowserTeam201603R  |  Actual Points:
Parent ID:  #15197                 |         Points:
 Reviewer:                         |        Sponsor:
-----------------------------------+------------------------------

Comment (by bugzilla):

 r=bugzilla
 replace {{{floor()}}} with {{{trunc()}}}
 remove {{{const double maxResolutionMs = 100;}}} and add {{{100.0}}}
 directly into the expression (as in other places).
 {{{return static_cast<double>(mEvent->time / 100)*100;}}} -> {{{return
 static_cast<double>(mEvent->time / 100) * 100.0;}}}
 {{{
 +    double now = static_cast<double>(PRMJ_Now() / PRMJ_USEC_PER_MSEC);
 +    return TimeClip(floor(now/100.0)*100.0);
 }}}
 to
 {{{
 return TimeClip(static_cast<double>(PRMJ_Now() / (PRMJ_USEC_PER_MSEC *
 100)) * 100.0);
 }}}
 >+    // Only expose milliseconds of accuracy, since ms is the smallest
 time unit
 >+    // for animations anyway.
 If it is used to measure FPS of animations, then 1000 FPS (1 ms) is enough
 for all fingerprinting needs. Maybe, standard 40 ms (25 FPS) is more
 suitable.
 > +  // Truncate all timers to microsecond accuracy
 Is this defense too weak?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18631#comment:4>
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