[tor-bugs] #23523 [Core Tor/Tor]: Handle extreme values better in add_laplace_noise()

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#23523: Handle extreme values better in add_laplace_noise()
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  teor
     Type:  defect                               |         Status:
                                                 |  needs_revision
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.3.x-final
Component:  Core Tor/Tor                         |        Version:  Tor:
                                                 |  0.2.6.2-alpha
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-relay, privcount, review-        |  Actual Points:
  group-24                                       |
Parent ID:  #23061                               |         Points:  0.5
 Reviewer:  catalyst                             |        Sponsor:
                                                 |  SponsorQ
-------------------------------------------------+-------------------------
Changes (by teor):

 * status:  needs_review => needs_revision


Comment:

 Replying to [comment:10 catalyst]:
 > I'm still looking over this. One thing that sticks out is that the
 comment in `get_min_safe_noise()` is inaccurate and caused me to
 misinterpret what it's actually doing on platforms with `DBL_MANT_DIG`
 less than 64.  It might be more correct to say "This is always safe,
 because floating point numbers are sign-magnitude and the negation of an
 exact number is also exact."

 All the types here are int64_t.

 But I agree the comment is confusing, particularly after I added a case
 that actually returns +/-INT64_MAX.

 Let's change it to:
 {{{
   tor_assert(get_max_safe_noise() >= 0);
   /* This is safe as long as get_max_safe_noise() is in 0..INT64_MAX,
 because -INT64_MAX..0 are representable as an int64_t. */
   return -get_max_safe_noise();
 }}}

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23523#comment:11>
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