[Bug math/688] Math error on a null sum operation: a =a + 0. !!

["laurent dot dagnac at atosorigin dot com" <sourceware-bugzilla at sources dot redhat dot com>]

------- Additional Comments From laurent dot dagnac at atosorigin dot com  2005-01-21 15:01 -------
Subject: Re: *** SPAM scored: Low ***  Math error on a null
 sum operation: a =a + 0.    !!

thank you for you help,

I modified my testcase in order to avoid the mentioned voilation, but
without resolving the problem.

double val;
char *c;

c = (char *) &val;
val = 100.00000005;
printf ("%2d %2d %2d %2d %2d %2d %2d %2d \n",
            *c, *(c+1), *(c+2),*(c+3),*(c+4),*(c+5),*(c+6),*(c+7));
val = val + 0.;
printf ("%2d %2d %2d %2d %2d %2d %2d %2d \n",
            *c, *(c+1), *(c+2),*(c+3),*(c+4),*(c+5),*(c+6),*(c+7));

Results...
 > -27 -81 53 0 0 0 89 64
 > 0 0 0 0 0 0 89 64

The fractional part (lower word of the double) has been avoided by the 
sum. !!

Can you help me again


jakub at redhat dot com a écrit :

> ------- Additional Comments From jakub at redhat dot com  2005-01-21 13:56 -------
> This has nothing to do with glibc FYI.
> Your testcase is invalid.
> Please study GCC manual about -fstrict-aliasing option (enabled at -O2 and above
> by default), you are violating that.  Furthermore, you really shouldn't overwrite
> random memory at ((char*)&val) - 1.
> 


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http://sources.redhat.com/bugzilla/show_bug.cgi?id=688

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