[tor-bugs] #24613 [Core Tor/Tor]: Avoid monotime_coarse_absolute_msec in channelpadding code

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#24613: Avoid monotime_coarse_absolute_msec in channelpadding code
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     Reporter:  nickm         |      Owner:  nickm
         Type:  enhancement   |     Status:  assigned
     Priority:  Medium        |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:  Sponsor8-can  |
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 As noted on #24374, `monotime_coarse_absolute_msec()` can be expensive on
 32-bit systems since it has to do a 64-bit division to compute msec.  We
 fixed the use of `monotime_coarse_absolute_msec` in `buf_t` and
 `packed_cell_t`, but we still have it in the channelpadding system.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24613>
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