RE: Expectations for 0/0
> -Original Message- > From: gcc-ow...@gcc.gnu.org [mailto:gcc-ow...@gcc.gnu.org] On Behalf > Of Paulo Matos > Sent: 29 July 2015 10:12 > To: Andrew Haley; gcc@gcc.gnu.org > Subject: RE: Expectations for 0/0 > > > > > -Original Message- > > From: Andrew Haley [mailto:a...@redhat.com] > > Sent: 28 July 2015 18:38 > > To: Paulo Matos; gcc@gcc.gnu.org > > Subject: Re: Expectations for 0/0 > > > > On 07/28/2015 04:40 PM, Paulo Matos wrote: > > > The block skips the test for ((unsigned int) xx << 1 == 0 && yy == > - > > 1), should we skip it if they're both zero as well? > > > > Yes. It's undefined behaviour. If we don't want to invoke nasal > > daemons we shouldn't do this. > > > Thanks. I will propose a patch to avoid this. > My mistake. The check is already in the test but as I simplified the test, I ended up removing the check for 0 in the denominator. Apologies. -- Paulo Matos
RE: Expectations for 0/0
> -Original Message- > From: Andrew Haley [mailto:a...@redhat.com] > Sent: 28 July 2015 18:38 > To: Paulo Matos; gcc@gcc.gnu.org > Subject: Re: Expectations for 0/0 > > On 07/28/2015 04:40 PM, Paulo Matos wrote: > > The block skips the test for ((unsigned int) xx << 1 == 0 && yy == - > 1), should we skip it if they're both zero as well? > > Yes. It's undefined behaviour. If we don't want to invoke nasal > daemons we shouldn't do this. Thanks. I will propose a patch to avoid this. -- Paulo Matos
Re: Expectations for 0/0
On 07/28/2015 04:40 PM, Paulo Matos wrote: > The block skips the test for ((unsigned int) xx << 1 == 0 && yy == -1), > should we skip it if they're both zero as well? Yes. It's undefined behaviour. If we don't want to invoke nasal daemons we shouldn't do this. Andrew.
Expectations for 0/0
Hi,
What are the expectations for the 0/0 division?
Test execute.exp=arith-rand.c generates two integers, both being 0 and one of
the testing blocks is:
{ signed int xx = x, yy = y, r1, r2;
if ((unsigned int) xx << 1 == 0 && yy == -1)
continue;
r1 = xx / yy;
r2 = xx % yy;
if (ABS (r2) >= (unsigned int) ABS (yy) || (signed int) (r1 * yy + r2)
!= xx)
abort ();
}
Our routine returns :
R1: 0x
R2: 0xf
Then it aborts because ABS (r2) >= (unsigned int) ABS (yy).
While I understand the results from our division routine might be peculiar,
this division is also undefined.
The block skips the test for ((unsigned int) xx << 1 == 0 && yy == -1), should
we skip it if they're both zero as well? If not, what do you expect to get from
0/0 and 0%0?
Regards,
Paulo Matos
