BIND 10 #1883: define tp_hash for some basic isc.dns classes

[BIND 10 Development]

#1883: define tp_hash for some basic isc.dns classes
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                   Reporter:         |                 Owner:  jinmei
  jinmei                             |                Status:  reviewing
                       Type:  task   |             Milestone:
                   Priority:  high   |  Sprint-20120717
                  Component:         |            Resolution:
  libdns++                           |             Sensitive:  0
                   Keywords:         |           Sub-Project:  DNS
            Defect Severity:  N/A    |  Estimated Difficulty:  5
Feature Depending on Ticket:         |           Total Hours:  0
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Comment (by jinmei):

 Replying to [comment:5 jelte]:
 > I had a comment about Py_hash_t but I see we already have #2026 for that
 (do we care about the implicit cast there, btw?) :)

 Hmm, not sure what exactly you meant by the implicit cast, but on
 looking into it more closely, I noticed we actually need to do care
 about it.  Py_hash_t is a signed integer, and tp_hash() is not
 expected to return -1.  So we need to ensure two things:
 - the conversion to Py_hash_t is safe (not result in an undefined
   behavior)
 - the result is never -1

 In the case of the extension to `RRType`, it's unlikely to be a real
 issue in practice because the original hash value is of uint16_t, and
 it size is quite likely to be smaller than sizeof(Py_hash_t).  But it
 could be more realistic concern for `Name` because the original hash
 is of size_t, and (in my environment) it has the same size as that of
 Py_hash_t.

 So I introduced a wrapper converter and used it for all existing
 cases.

 > I have one tiny suggestion for the unit tests; add
 > {{{
 >         self.assertEqual(hash(RRType.AAAA()), hash(RRType("Type28")))
 > }}}
 > as well (or a similar one).

 Okay, added.

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Ticket URL: <http://bind10.isc.org/ticket/1883#comment:6>
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