[GiNaC-list] A strange behaviour while implementing archive in auser-defined class

[Feng Feng]

Thanks very much for the patch!


And again thanks a lot for the suggestions for Symbol::calchash,
that is really what I am looking for!


Best regards!
Feng


在 2021年12月20日 16:57，Oleg Finkelshteyn<olegfink at gmail.com> 写道：


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. Feng: regardless of this bug, i think you'll want something like following: unsigned Symbol::calchash() const { hashvalue = get_symbol(get_name()).gethash(); setflag(status_flags::hash_calculated); return hashvalue; } 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 > https://www.ginac.de/mailman/listinfo/ginac-list
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