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[Imgcif-l] Update: Possible bug in cbf_byte_offset.c

  • To: imgcif-l@iucr.org
  • Subject: [Imgcif-l] Update: Possible bug in cbf_byte_offset.c
  • From: "Herbert J. Bernstein" <yaya@bernstein-plus-sons.com>
  • Date: Sun, 21 Feb 2010 12:37:21 -0500
  • In-Reply-To: <4B7D3610020000C80005E79E@hermes.dowling.edu>
  • References: <4B7D3610020000C80005E79E@hermes.dowling.edu>
Dear Colleagues,

   There is a difficult to provoke bug in the CBFlib byte offset code.
It arises in handling 16 bit images (not 32 bit images) in which the
difference between two adjacent pixel values is -32768.  I hope to
have a fully tested update later this coming week.  The problem is
that the 16-bit code did not catch a delta of 0x8000 and escape it.

   I do not think you will see anything equivalent to this for
31-bit images (e.g. from the Pilatus 6M), even when there is an abrupt
transition in pixel values, but I am rechecking that code and
adding test cases just to be certain.

   Our thanks for Nick Sauter for starting us on tracing this bug.

   Regards,
     Herbert


At 12:44 PM -0500 2/18/10, Herbert J. Bernstein wrote:
>To: imgcif-l@iucr.org
>From: "Herbert J. Bernstein" <yaya@bernstein-plus-sons.com>
>Subject: Re: [Imgcif-l] Fwd: Re:  Possible bug in cbf_byte_offset.c
>
>Dear Graeme,
>
>    Yup.  I agree.  I am working on a see-saw image to cover a very 
>wide range of
>both positive and negative delta's tp try to flush out any other such
>bugs.  I would appreciate your 128x128, but I also want to do a much
>larger one to catch the 32 bit image cases.
>
>    Regards,
>      Herbert
>At 11:06 AM -0500 2/18/10, Herbert J. Bernstein wrote:
>  >To: <imgcif-l@iucr.org>, <nksauter@lbl.gov>
>  >Subject: Re: [Imgcif-l] Possible bug in cbf_byte_offset.c
>  >
>>Dear Herbert,
>>
>>Surely it would be relatively straightforward to "fake" some
>>pathalogical images for the purposes of testing, i.e. set values of
>>0xffff, 0x0000, 0xffff, 0x0000 &c. in a "C" array and compress this to a
>>CBF stream?
>>
>>As you could have a valid CBF 128 x 128 pixels (say) it needn't be that
>>large even... If I get a quiet moment I'll code something up.
>>
>>Best wishes,
>>
>>Graeme
>>
>>-----Original Message-----
>>From: imgcif-l-bounces@iucr.org [mailto:imgcif-l-bounces@iucr.org] On
>>Behalf Of Herbert J. Bernstein
>>Sent: 18 February 2010 04:21
>>To: Nicholas K. Sauter
>>Cc: imgcif-l@iucr.org
>>Subject: Re: [Imgcif-l] Possible bug in cbf_byte_offset.c
>>
>>Dear Nick,
>>
>>     You are absolutely right.  I am also having trouble working up a test
>>case.  It needs an image with a very large negative delta.   I'll try
>>to force something.
>>
>>     In the meantime, I have updated the sourceforge cbflib svn with the
>>fix in CBFlib_bleeding_edge.  After I have a test case, I'll propagate
>>the change more widely.
>>
>>     I am copying this to the imgCIF list to warn others in the meantime.
>>
>>     Thank you very much.  Well done.
>>
>>     Regards,
>>       Herbert
>>
>>
>>
>>
>>At 11:06 AM -0800 2/17/10, Nicholas K. Sauter wrote:
>>>Herbert,
>>>
>>>Please see line 1166 in src/cbf_byte_offset.c.
>>>
>>>Based on the logic of the algorithm I think this line should be
>>>
>>>if (delta[0] & 0x8000) {
>>>
>>>i.e., there is an extra "0" in the hex value in the CVS code.
>>>That being said, I don't think this line has an effect on any of my
>>>test cases, so I'm at a loss about how to test this out.
>>>
>>>Nick
>>
>>
>>--
>>=====================================================
>>    Herbert J. Bernstein, Professor of Computer Science
>>      Dowling College, Kramer Science Center, KSC 121
>>           Idle Hour Blvd, Oakdale, NY, 11769
>>
>>                    +1-631-244-3035
>>                    yaya@dowling.edu
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>--
>=====================================================
>   Herbert J. Bernstein, Professor of Computer Science
>     Dowling College, Kramer Science Center, KSC 121
>          Idle Hour Blvd, Oakdale, NY, 11769
>
>                   +1-631-244-3035
>                   yaya@dowling.edu
>=====================================================
>_______________________________________________
>imgcif-l mailing list
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>http://scripts.iucr.org/mailman/listinfo/imgcif-l


-- 
=====================================================
  Herbert J. Bernstein, Professor of Computer Science
    Dowling College, Kramer Science Center, KSC 121
         Idle Hour Blvd, Oakdale, NY, 11769

                  +1-631-244-3035
                  yaya@dowling.edu
=====================================================
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