[GiNaC-list] A strange behaviour while implementing archive in a user-defined class
ovf
ovf at mm.st
Mon Dec 20 09:48:54 CET 2021
i suspect this is actually due to a typo in relational::compare_same_type.
(basic reality check: pathologic (e.g. constant) hash functions should lead to degraded performance, not different results)
diff --git a/ginac/relational.cpp b/ginac/relational.cpp
index 599a2635..dbc541a3 100644
--- a/ginac/relational.cpp
+++ b/ginac/relational.cpp
@@ -223,8 +223,8 @@ int relational::compare_same_type(const basic & other) const
return (o < oth.o) ? -1 : 1;
break;
}
- const int lcmpval = lh.compare(oth.rh);
- return (lcmpval!=0) ? lcmpval : rh.compare(oth.lh);
+ const int lcmpval = lh.compare(oth.lh);
+ return (lcmpval!=0) ? lcmpval : rh.compare(oth.rh);
}
attached is also a shorter test along the same lines as Feng's.
it prints the result of comparing two symbol==0 expressions to each other both ways.
without the patch, the output is -1 -1 (which is inconsistent), and with the patch it's -1 1.
a hash collision is needed to elicit this bug because basic::compare returns early without calling compare_same_type if hashes differ.
thanks
On Sat, 18 Dec 2021, at 11:10, Vladimir V. Kisil wrote:
>>>>>> On Sat, 18 Dec 2021 16:22:22 +0800, Feng Feng <f.feng at outlook.com> said:
> FF> I got a strange behaviour while implementing the archive in
> FF> user-defined class, to make the behaviour more explicitly, let
>
> If you will delete the method Symbol::calchash() from your class you
> will get the expected behaviour.
> --
> Vladimir V. Kisil http://www.maths.leeds.ac.uk/~kisilv/
> Book: Geometry of Mobius Maps https://doi.org/10.1142/p835
> Soft: Geometry of cycles http://moebinv.sourceforge.net/
> Jupyter notebooks: https://github.com/vvkisil?tab=repositories
>>>>>> On Sat, 18 Dec 2021 16:22:22 +0800, Feng Feng <f.feng at outlook.com> said:
>
> FF> Dear all,
>
>
> FF> I got a strange behaviour while implementing the archive in
> FF> user-defined class, to make the behaviour more explicitly, let
> FF> me post the C++ code here:
>
>
> FF> #include <ginac/ginac.h> #include <fstream>
>
>
> FF> using namespace GiNaC; using namespace std;
>
>
> FF> class Symbol : public symbol {
> FF> GINAC_DECLARE_REGISTERED_CLASS(Symbol, symbol) public:
> FF> Symbol(const string &s); void archive(archive_node & n) const
> FF> override; void read_archive(const archive_node& n, lst& sym_lst)
> FF> override; unsigned calchash() const override; };
> FF> GINAC_DECLARE_UNARCHIVER(Symbol);
>
>
> FF> GINAC_IMPLEMENT_REGISTERED_CLASS(Symbol, symbol)
> FF> GINAC_BIND_UNARCHIVER(Symbol);
>
>
> FF> const symbol & get_symbol(const string & s) { static map<string,
> FF> symbol> dict; if (dict.find(s) == dict.end()) dict[s] =
> FF> symbol(s); return dict[s]; }
>
>
> FF> Symbol::Symbol() { } Symbol::Symbol(const string &s) :
> FF> symbol(get_symbol(s)) { } int Symbol::compare_same_type(const
> FF> basic &other) const { const Symbol &o = static_cast<const Symbol
> FF> &>(other); int ret = get_name().compare(o.get_name());
> FF> if(ret==0) return 0; else if(ret<0) return -1; else return 1; }
>
> FF> void Symbol::archive(archive_node & n) const {
> FF> inherited::archive(n); }
>
> FF> void Symbol::read_archive(const archive_node& n, lst& sym_lst) {
> FF> inherited::read_archive(n, sym_lst); *this = Symbol(get_name());
> FF> }
>
>
> FF> unsigned Symbol::calchash() const { static auto hash =
> FF> symbol("_").gethash(); return hash; }
>
>
> FF> int main() { Symbol k1("k1"), k2("k2"); auto garfn = "tmp.gar";
>
> FF> { archive ar; ex val = lst{ k1*k1, k2*k2 };
> FF> ar.archive_ex(val, "key"); ofstream out(garfn); out << ar;
> FF> out.close(); cout << "writed: " << val << endl; } { archive ar;
> FF> ifstream in(garfn); in >> ar; in.close(); auto val =
> FF> ar.unarchive_ex(lst{}, "key"); cout << "read: " << val << endl;
> FF> } // console output is // writed: {k1^2,k2^2} // read:
> FF> {k1^2,k2^2}
>
> FF> { archive ar; ex val = lst{ k1*k1==0, k2*k2==0 };
> FF> ar.archive_ex(val, "key"); ofstream out(garfn); out << ar;
> FF> out.close(); cout << "writed: " << val << endl; } { archive ar;
> FF> ifstream in(garfn); in >> ar; in.close(); auto val =
> FF> ar.unarchive_ex(lst{}, "key"); cout << "read: " << val << endl;
> FF> } // console output is // writed: {k1^2==0,k2^2==0} // read:
> FF> {k1^2==0,k1^2==0} // Note that the last line above, both items
> FF> are the same: k1^2==0
>
> FF> return 0; }
>
>
> FF> Here I want to introduce a class Symbol, when one defines Symbol
> FF> a(“a”), b(“a”);, then a and b will be the same or equal, so I
> FF> override the method compare_same_type.
>
>
>
>
> FF> The last console output seems very strange to me, the both items
> FF> are the same, while the expected result is "read:
> FF> {k1^2==0,k2^2==0}”.
>
>
> FF> Thanks very much!
>
>
> FF> Best regards! Feng
>
> FF> ----------------------------------------------------
> FF> Alternatives:
>
> FF> ----------------------------------------------------
> FF> _______________________________________________ GiNaC-list
> FF> mailing list GiNaC-list at ginac.de
> FF> https://www.ginac.de/mailman/listinfo/ginac-list
> _______________________________________________
> GiNaC-list mailing list
> GiNaC-list at ginac.de
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