Thread

1. Bug in intarray?

   Guillaume Lelarge <guillaume@lelarge.info> — 2012-02-16T21:43:48Z

   Hi,
   
   On a french PostgreSQL web forum, one of our users asked about a curious
   behaviour of the intarray extension.
   
   This query:
     SELECT ARRAY[-1,3,1] & ARRAY[1, 2];
   should give {1} as a result.
   
   But, on HEAD (and according to his tests, on 9.0.6 and 9.1.2), it
   appears to give en empty array.
   
   Digging on this issue, another user (Julien Rouhaud) made an interesting
   comment on this line of code:
   
   if (i + j == 0 || (i + j > 0 && *(dr - 1) != db[j]))
   
   (line 159 of contrib/intarray/_int_tool.c, current HEAD)
   
   Apparently, the code tries to check the current value of the right side
   array with the previous value of the resulting array. Which clearly
   cannot work if there is no previous value in the resulting array.
   
   So I worked on a patch to fix this, as I think it is a bug (but I may be
   wrong). Patch is attached and fixes the issue AFAICT.
   
   Thanks.
   
   
   -- 
   Guillaume
   http://blog.guillaume.lelarge.info
   http://www.dalibo.com
   

2. Re: Bug in intarray?

   Tom Lane <tgl@sss.pgh.pa.us> — 2012-02-17T00:27:57Z

   Guillaume Lelarge <guillaume@lelarge.info> writes:
   > This query:
   >   SELECT ARRAY[-1,3,1] & ARRAY[1, 2];
   > should give {1} as a result.
   
   > But, on HEAD (and according to his tests, on 9.0.6 and 9.1.2), it
   > appears to give en empty array.
   
   Definitely a bug, and I'll bet it goes all the way back.
   
   > Digging on this issue, another user (Julien Rouhaud) made an interesting
   > comment on this line of code:
   
   > if (i + j == 0 || (i + j > 0 && *(dr - 1) != db[j]))
   
   > (line 159 of contrib/intarray/_int_tool.c, current HEAD)
   
   > Apparently, the code tries to check the current value of the right side
   > array with the previous value of the resulting array. Which clearly
   > cannot work if there is no previous value in the resulting array.
   
   > So I worked on a patch to fix this, as I think it is a bug (but I may be
   > wrong). Patch is attached and fixes the issue AFAICT.
   
   Yeah, this code is bogus, but it's also pretty unreadable.  I think
   it's better to get rid of the inconsistently-used pointer arithmetic
   and the fundamentally wrong/irrelevant test on i+j, along the lines
   of the attached.
   
   			regards, tom lane
   
   
   

3. Re: Bug in intarray?

   Guillaume Lelarge <guillaume@lelarge.info> — 2012-02-17T08:42:07Z

   On Thu, 2012-02-16 at 19:27 -0500, Tom Lane wrote:
   > Guillaume Lelarge <guillaume@lelarge.info> writes:
   > > This query:
   > >   SELECT ARRAY[-1,3,1] & ARRAY[1, 2];
   > > should give {1} as a result.
   > 
   > > But, on HEAD (and according to his tests, on 9.0.6 and 9.1.2), it
   > > appears to give en empty array.
   > 
   > Definitely a bug, and I'll bet it goes all the way back.
   > 
   > > Digging on this issue, another user (Julien Rouhaud) made an interesting
   > > comment on this line of code:
   > 
   > > if (i + j == 0 || (i + j > 0 && *(dr - 1) != db[j]))
   > 
   > > (line 159 of contrib/intarray/_int_tool.c, current HEAD)
   > 
   > > Apparently, the code tries to check the current value of the right side
   > > array with the previous value of the resulting array. Which clearly
   > > cannot work if there is no previous value in the resulting array.
   > 
   > > So I worked on a patch to fix this, as I think it is a bug (but I may be
   > > wrong). Patch is attached and fixes the issue AFAICT.
   > 
   > Yeah, this code is bogus, but it's also pretty unreadable.  I think
   > it's better to get rid of the inconsistently-used pointer arithmetic
   > and the fundamentally wrong/irrelevant test on i+j, along the lines
   > of the attached.
   > 
   
   Completely agree.
   
   Thank you.
   
   
   -- 
   Guillaume
   http://blog.guillaume.lelarge.info
   http://www.dalibo.com