#19928: doctest fix for infinities break the hash contract
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Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.1
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: Fixed upstream, in a later | Work issues:
stable release. | Commit:
Branch: | Stopgaps:
Dependencies: |
-------------------------------------------------+-------------------------
Changes (by rws):
* upstream: N/A => Fixed upstream, in a later stable release.
* dependencies: #19927 =>
Old description:
> {{{
> sage: hash(-oo)
> -9223372036854775808
> sage: hash(SR(-oo))
> 1390175631
> sage: hash(oo)
> 9223372036854775807
> sage: hash(SR(oo))
> 1577573780
> sage: hash(unsigned_infinity)
> 9223372036854775806
> sage: hash(SR(unsigned_infinity))
> 2904791665
> }}}
> The reason is that (at least with `-oo`) in Pynac they can be represented
> as an `expair` and such hashes are calculated using
> `all^(rest^coeff)^overall_coeff`.
>
> So the question is also why Pynac needs an `expair` for `oo` but not for
> `pi`:
> {{{
> sage: SR(1*pi)._dbgprinttree()
> pi (constant) @0x2844e00, hash=0xa6ee0bd1, flags=0xf
> sage: SR(oo)._dbgprinttree()
> infinity (infinity) @0x1e78ef0, hash=0x0, flags=0x7
> 1 (numeric) @0x1cbe380, hash=0x5a00e46d, flags=0x7
> }}}
> See https://github.com/pynac/pynac/issues/126
New description:
{{{
sage: hash(-oo)
-9223372036854775808
sage: hash(SR(-oo))
1390175631
sage: hash(oo)
9223372036854775807
sage: hash(SR(oo))
1577573780
sage: hash(unsigned_infinity)
9223372036854775806
sage: hash(SR(unsigned_infinity))
2904791665
}}}
Fixed in https://github.com/pynac/pynac/issues/126
--
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Ticket URL: <http://trac.sagemath.org/ticket/19928#comment:5>
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