#19928: 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: N/A | Work issues:
Branch: | Commit:
Dependencies: #19927 | Stopgaps:
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Description changed by rws:
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`.
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
}}}
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
}}}
--
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Ticket URL: <http://trac.sagemath.org/ticket/19928#comment:3>
Sage <http://www.sagemath.org>
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