* Rafael Laboissiere <raf...@debian.org> [2009-06-14 15:39]:
> * Rafael Laboissiere <raf...@debian.org> [2009-06-14 12:25]:
>
> > I think that the different values of x_max and x_min explain the bug on
> > the mips system. I guess that this is caused by the following lines in
> > pr-output.cc (function set_format):
> >
> > int x_max = max_abs == 0.0
> >
> > ? 0 : static_cast<int> (floor (log10 (max_abs) + 1.0));
> >
> >
> >
> > int x_min = min_abs == 0.0
> >
> > ? 0 : static_cast<int> (floor (log10 (min_abs) + 1.0));
> >
>
> I meant lines 854 to 858 in pr-output.cc, in function
> set_format (const Complex& c, int& r_fw, int& i_fw)
I think I found the cause of the bug. The simple program:
///////////////////////////////////////////////////////////////////////////
#include <cmath>
#include <iostream>
int
main (void)
{
std::cerr << static_cast<int> (floor (log10 (0.0/0.0))) << std::endl;
return 0;
}
///////////////////////////////////////////////////////////////////////////
when compiled on mips yields 2147483647, while on amd64 and i386 it
yields -2147483648. This explains the different behavior on both
architectures.
Now, I am wondering whether the code in set_format() makes sense. The
function reads:
///////////////////////////////////////////////////////////////////////////
static void
set_format (const Complex& c, int& r_fw, int& i_fw)
{
// [snip]
double rp = c.real ();
double ip = c.imag ();
bool inf_or_nan = (xisinf (c) || xisnan (c));
bool int_only = (D_NINT (rp) == rp && D_NINT (ip) == ip);
double r_abs = rp < 0.0 ? -rp : rp;
double i_abs = ip < 0.0 ? -ip : ip;
int r_x = r_abs == 0.0
? 0 : static_cast<int> (floor (log10 (r_abs) + 1.0));
// [snip]
///////////////////////////////////////////////////////////////////////////
When r_abs is NaN (as in the bug-triggering case) what is the sense of
computing log10 (r_abs) and propagating the result? I am probably
missing something but it seems just pure chance that r_x ends up being
negative on amd64 and i386, what does not trigger the bug.
--
Rafael
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