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digitalmars.D.bugs - [Issue 7836] New: NaNs inside associative array don't use normal FP equality

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7836

           Summary: NaNs inside associative array don't use normal FP
                    equality
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: wrong-code
          Severity: normal
          Priority: P2
         Component: druntime
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



I don't know if this is a bug, or if here D/DMD is working as designed. I am
not sure.

This code shows that floating point NaNs are not tested with == inside
associative arrays (because NaNs != NaNs):

import std.stdio: writeln;
void main() {
    int[double] aa;
    aa[double.nan] = 1;
    writeln(aa);
    aa[double.nan] = 2;
    writeln(aa);
}


Output DMD 2.059beta:

[nan:1]
[nan:2]



Python uses == to compare dict (associative array) keys, so NaNs can't
overwrite each other:


 a = {}
 a[float("nan")] = 1
 a






{nan: 1}

 a[float("nan")] = 2
 a






{nan: 1, nan: 2}


So maybe DMD has to act as Python in this case.

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Apr 05 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7836


hsteoh quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hsteoh quickfur.ath.cx



This is an AA implementation bug. Internally, AA's use bitwise comparison,
which is wrong in many cases.

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Apr 14 2012
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7836


hsteoh quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         OS/Version|Windows                     |All



Actually, this bug has nothing to do with AA's. The problem is that double's
typeinfo.equals and typeinfo.compare does not respect NaNs:

import std.stdio: writeln;
void main() {
    double x = double.nan, y = double.nan;
    writeln(x == y); // prints false (OK)
    writeln(typeid(double).equals(&x, &y)); // prints true (WRONG)
    writeln(typeid(double).compare(&x, &y)); // prints 0 (WRONG)
}

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Jul 08 2013