[ECOS] issue with floor()

[David Brennan]

See results below

On Wed, Nov 10, 2010 at 6:34 AM, David Brennan <david@brennanhome.com> wrote:
> Thank you Paul,
>
> On Wed, Nov 10, 2010 at 12:08 AM, Paul D. DeRocco
> <pderocco@ix.netcom.com> wrote:
>>> From: David Brennan
>>>
>>> I am using a relatively recent CVS of eCos on an x86 VME
>>> target. I am trying to get an existing application working,
>>> and I stumbled across an unusual result.
>>>
>>> The code called floor() with a value of 0.048000000000000001.
>>> the correct return value should have been 0.0.
>>>
>>> Single stepping through the "bit twiddling" looked like it
>>> was pursuing the correct code path, but at this point,
>>> somthing went wrong.
>>>
>>> 97                    if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
>>> (gdb) s
>>> 98                        if(i0>=0) {i0=i1=0;}
>>> (gdb) p i0
>>> $4 = 8
>>> (gdb) s
>>> 131   }
>>> (gdb) info locals
>>> i0 = 8
>>> j0 = -5
>>> i = 1067989024
>>> x = 0.048000000000000001
>>> (gdb) li
>>> 126               }
>>> 127           }
>>> 128           CYG_LIBM_HI(x) = i0;
>>> 129           CYG_LIBM_LO(x) = i1;
>>> 130           return x;
>>> 131   }
>>> 132
>>> 133   #endif // ifdef CYGPKG_LIBM
>>> 134
>>> 135   // EOF s_floor.c
>>>
>>> It appears that the code did not run line 98 correctly.
>>
>> <snip>
>>
>>> I am using a compiler that I built (so that is most likely
>>> the problem). I am using OS X for my host, and there are not
>>> pre-built binaries for that.
>>
>> I would think examining the assembly language would clear up the mystery,
>> especially if you find the problem persists with optimization turned off.
>> For instance, it could be that the arithmetic doesn't work because
>> something's busted in the FP support, but the sign test works correctly
>> because it doesn't use an FP instruction to test the sign.
>>
>> --
>>
>> Ciao,               Paul D. DeRocco
>> Paul                mailto:pderocco@ix.netcom.com
>>
>
<snip>
>
> I will re-run the floor test later today without optimization. But if
> that solves the problem, then what? Is this a gcc bug? Or a gcc
> configuration error?
>
> Thanks again for your help
> David Brennan
>

Turning off optimization allows the floor test to pass.


(gdb) c
Continuing.
INFO:<Starting tests from testcase
/opt/ecos-old/eCosIRL/OS/ecos/packages/language/c/libm/current/tests/vectors/floor.c
for Math library floor() function>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
INFO:<Still crunching, please wait...>
PASS:<floor() is stable>
EXIT:<Finished tests from testcase
/opt/ecos-old/eCosIRL/OS/ecos/packages/language/c/libm/current/tests/vectors/floor.c
for Math library floor() function>

This will let me continue on my project. But I would like for
optimization to work. What is the best method for approaching gcc
maintainers about this issue?

Thank you for your help
David Brennan

--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss