Re: 3.0.1 release?

[Michael Goffioul]

On Tue, Apr 8, 2008 at 5:11 PM, David Bateman
<address@hidden> wrote:
>  Yes this is the issue... It seems the bitmax under windows if not
>  returning the right value.. bitmax uses
>
>  static_cast<double> (0x1FFFFFFFFFFFFFLL)
>
>  as its definition and so perhaps its the "LL" at the end that is causing
>  the issue as it really should be a "UL".. Can you try
>
>  #include <iostream>
>
> int main (void)
>  {
>         uint64_t a = 0x001FFFFFFFFFFFFFUL^0x0007FFFFFFFFFFFFUL;
>     double b = static_cast<double> (0x1FFFFFFFFFFFFFLL);
>     double c = static_cast<double> (0x1FFFFFFFFFFFFFUL);
>
>     std::cerr << 0x001FFFFFFFFFFFFFUL << std::endl;
>     std::cerr << 0x0007FFFFFFFFFFFFUL << std::endl;
>         std::cerr << a  << std::endl;
>         std::cerr << b  << std::endl;
>         std::cerr << c  << std::endl;
>         std::cerr << b - c  << std::endl;
>         return 0;
>  }
>
>  and see whether the last result is something other than zero.. If so I
>  think we've found the issue.

I don't think so: the last result is effectively zero. I tracked down a little
bit the problem and what I discovered is that bitmax returns the correct
result, that is

9007199254740991

but when casting this double value to uint64, then it becomes

9007199254740992

When debugging the "cast" call, I end up calling

octave_int<uint64_t>(double d), which calls xround. As MSVC does
not have native round, xround code is:

return x > 0 ? floor (x + 0.5) : ceil (x - 0.5);

This effectively adds 1 when x is equal to bitmax.

At this point, I don't now what to do. If there's not quick solution for
this problem, John, then I'd say release 3.0.1 with the problem. I don't
think this is a critical problem as it seems to only happen in this
specific corner case (when using bitmax). For instance:

octave.exe:9> cast(bitmax, 'uint64')
ans = 9007199254740992
octave.exe:10> cast(bitmax-1, 'uint64')
ans = 9007199254740990

Now, something I'm not sure is whether this is really the cause of the
test failure that started this thread. David, do you have an idea?

Michael.