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digitalmars.D.bugs - [Issue 4988] New: Floats in structs are not equal on 0.0f vs -0.0f

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4988

           Summary: Floats in structs are not equal on 0.0f vs -0.0f
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Keywords: wrong-code
          Severity: critical
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: simen.kjaras gmail.com


--- Comment #0 from Simen Kjaeraas <simen.kjaras gmail.com> 2010-10-04 01:34:30
PDT ---
The following code asserts:

struct Foo {
    float data;
}

void bug( ) {
    assert( Foo( 0.0f ) == Foo( -0.0f ) ); // Works fine
    auto a = Foo( 0.0f );
    auto b = Foo( -0.0f );
    assert( b == a ); // Asserts
}

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Oct 04 2010
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4988


Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au


--- Comment #1 from Don <clugdbug yahoo.com.au> 2010-10-06 23:57:21 PDT ---
This also applies to NaNs:

    assert( Foo( float.nan ) != Foo( float.nan ) ); // Works fine
    auto a = Foo( float.nan );
    auto b = Foo( float.nan );
    assert( b != a ); // Asserts

The real problem is e2ir.c, line 2313, EqualExp::toElem(), which does a bitwise
compare for structs. That isn't valid if there are floating point numbers
inside.
This is a pain, because it needs to be considered recursively.

A quick-and-dirty fix would be to construct an opEquals whenever this happens:

clone.c StructDeclaration::needOpEquals() line 106.

        if (tv->ty == Tstruct)
        {   TypeStruct *ts = (TypeStruct *)tv;
            StructDeclaration *sd = ts->sym;
            if (sd->eq)
                goto Lneed;
        }
+        if (tv->isfloating())
+            goto Lneed;
    }
Ldontneed:

But the problem with this is that it slows down all equality tests involving
floats. Maybe the inliner can take care of it, but generally I don't think it's
an acceptable solution.

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Oct 06 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4988


bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc


--- Comment #2 from bearophile_hugs eml.cc 2010-10-07 04:21:33 PDT ---
Performance is important, but correct semantics is more important.

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Oct 07 2010
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4988


Simen Kjaeraas <simen.kjaras gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE


--- Comment #3 from Simen Kjaeraas <simen.kjaras gmail.com> 2011-02-03 04:40:44
PST ---
*** This issue has been marked as a duplicate of issue 3789 ***

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Feb 03 2011