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From "Stefan Teleman" <stefan.tele...@gmail.com>
Subject Re: [jira] Created: (STDCXX-862) [Sun C++ 5.9] 0.char test failed due to different binary representation of "long double ld1 = 0" and "long double ld2 = 0."
Date Tue, 15 Apr 2008 19:09:50 GMT
On Tue, Apr 15, 2008 at 2:30 PM, Martin Sebor <sebor@roguewave.com> wrote:

> > > Farid Zaripov (JIRA) wrote:
> > >
> > > > [Sun C++ 5.9] 0.char test failed due to different binary
> representation of "long double ld1 = 0" and "long double ld2 = 0."
> > > >
> > >
> >
> >
> > > This feels like compiler bug, wouldn't you say?
> > >
> >
> >  I don't know. The both long doubles behaves as zero. The only comparing
> them with memcmp() gives the wrong result.
> >
>
>  I thought there was just one bit pattern for a positive floating
>  point 0 in IEE 754, namely all bits clear.
>
>  Martin

// testlongdouble.cc
//
#include <iostream>
#include <cstdlib>
using namespace std;

#include <stdlib.h>

int
main(int argc, char* argv[])
{
    long double x;
    long double y;

    x = static_cast<long double>(drand48());
    y = static_cast<long double>(drand48());

    std::cerr << "x = " << x << " y = " << y << endl;
    std::cerr << "sizeof(x) = " << sizeof(x) << " sizeof(y) = " <<
sizeof(y) << endl;
    std::cerr << "sizeof(x) == sizeof(y): " << ((sizeof(x) ==
sizeof(y)) ? "TRUE" : "FALSE") << endl;

    x = 0;
    y = 0.;

    std::cerr << "x = " << x << " y = " << y << endl;
    std::cerr << "sizeof(x) = " << sizeof(x) << " sizeof(y) = " <<
sizeof(y) << endl;
    std::cerr << "sizeof(x) == sizeof(y): " << ((sizeof(x) ==
sizeof(y)) ? "TRUE" : "FALSE") << endl;

    return 0;
}

//

>> CC -V
CC: Sun C++ 5.9 SunOS_i386 Patch 124864-01 2007/07/25
>> ./testlongdouble
x = 0.396465 y = 0.840485
sizeof(x) = 12 sizeof(y) = 12
sizeof(x) == sizeof(y): TRUE
x = 0 y = 0
sizeof(x) = 12 sizeof(y) = 12
sizeof(x) == sizeof(y): TRUE

http://developers.sun.com/sunstudio/downloads/patches/ss12_patches.jsp

There are more recent patches than my own installation.

--Stefan

-- 
Stefan Teleman
KDE e.V.
stefan.teleman@gmail.com

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