[Insight-developers] vnl updates

[Tom Vercauteren]

Hey Luis,

These issues are most certainly related to how half integers are
rounded by vnl_math_round. As specified by the until test of vnl, the
result of vnl_math_round(12.5) could either be 12 or 13. Within ITK, I
think that it is assumed that half integers are rounded to away from
zero, e.g. vnl_math_round(12.5)==13. With the version of vnl_math.h
that ships with ITK, this should be true on every platform except 32
bits windows using MSVC (half integers rounded to nearest even
integer). This behavior has been modified in vnl cvs version. Most
platform will now round half integers to the nearest even integer, ie
vnl_math_round(12.5)==12 and vnl_math_round(11.5)==12.

This may explain the test failures. One thing that I didn't check is
whether the test that are failing in your experimental build are also
failing with the current version of ITK on 32 bits windows using MSVC.

Since, in the version that ships with ITK, the semantic of
vnl_math_round for half integer was not strictly enforced and not
consistent across the platforms, I took the liberty of choosing the
most efficient one depending on the platform (round half integers to
the nearest even integer is now the most common). Does this look like
a problem to you? We could maybe simply make the unit tests in ITK a
little more permissive to make them pass no matter how half integers
are rounded by vnl_math_round.

Hope this helps.

Regards,
Tom


On Mon, Dec 29, 2008 at 11:45 PM, Luis Ibanez <luis.ibanez at kitware.com> wrote:
>
> Hi Tom,
>
> The Experimental build (From Ubuntu Linux with gcc 4.2):
>
> http://www.cdash.org/CDash/viewSite.php?siteid=1086&project=2&currenttime=1230512400
>
> came up with three failing tests.
>
> http://www.cdash.org/CDash/viewTest.php?onlyfailed&buildid=239928
>
> They are:
>
>     760 - itkInterpolateTest (Failed)
>     1310 - ResampleImageFilter3Test1 (Failed)
>     1314 - ResampleImageFilter9Test (Failed)
>
>
> We will have to address these failure before we
> update the vnl_math.h file.
>
>
> Would you have a chance to look at one of them ?
>
> The first one and third one seem to be the ones providing a better hint
> to the source of the problem.
>
> In particular, the diff image at
> http://www.cdash.org/CDash/testDetails.php?test=14663712&build=239928
> may help.
>
>
>    Please let us know,
>
> ----------------------------------------------------------------------------------------------
> On Mon, Dec 29, 2008 at 12:27 PM, Luis Ibanez <luis.ibanez at kitware.com>
> wrote:
>>
>> Hi Tom,
>>
>> Thanks for looking at this.
>>
>> I'm running an experimental build with this change (new vnl_math.h).
>>
>> If it comes out green I'll commit the new vnl_math.h file,
>> and we will see the effect on tomorrow's Nightly builds...
>>
>>
>>       Luis
>>
>>
>>
>> -------------------------------------------------------------------------------------------------------
>> On Mon, Dec 29, 2008 at 12:24 PM, Tom Vercauteren
>> <tom.vercauteren at m4x.org> wrote:
>>>
>>> Small mistake... I meant VNL_CONFIG_ENABLE_SSE2_ROUNDING will not be
>>> defined by cmake.
>>> Tom
>>>
>>> On Mon, Dec 29, 2008 at 6:04 PM, Tom Vercauteren
>>> <tom.vercauteren at m4x.org> wrote:
>>> >> Could you point me to the set of lines that we want to import
>>> >> from the new version of vnl_math.h  ?
>>> >
>>> > The difference between ITK's vnl_math.h and vxl's vnl_math.h is
>>> > exactly what is needed:
>>> >
>>> > http://vxl.cvs.sourceforge.net/viewvc/vxl/vxl/core/vnl/vnl_math.h?r1=1.50&r2=1.42
>>> >
>>> > So the only thing that needs to be done is replace the current
>>> > vnl_math.h file by the most up-to-date one.
>>> >
>>> > As I mentioned, the sse2 optimization will not be compiled since
>>> > VNL_CHECK_FPU_ROUNDING_MODE will not be defined by cmake.
>>> >
>>> >
>>> >> We could insert them today or tomorrow...
>>> >
>>> > Great!
>>> >
>>> > Thanks,
>>> > Tom
>>> >
>>> > P.S.: As far as vnl_math.h is concerned, there should be no backward
>>> > compatibility issue.
>>> >
>>
>
>