numpy-discussion

[Numpy-discussion] [OT] Can anybody else reproduce this ? (but in ctypes)

[David C. <da...@ar...>]

Hi,

    This is a bit OT, but I wasted quite some time on this time, when 
using 64 bits integers and ctypes on ubuntu edgy. As I know other people 
use ubuntu with numpy, this may save some headache to others. I found 
this behaviour which looks like a bug in ctypes for python2.5 on edgy 
ubuntu:

    python2.5 -c "from ctypes import sizeof, c_longlong; print 
sizeof(c_longlong)"

    prints 4 instead of 8, which in my case is problematic for 
structures alignement. This affects only python2.5, and does not affect 
a python installed from sources. Can anybody else reproduce this ?

    cheers,

    David

Re: [Numpy-discussion] [OT] Can anybody else reproduce this ? (but in ctypes)

[Robert K. <rob...@gm...>]

David Cournapeau wrote:
> Hi,
> 
>     This is a bit OT, but I wasted quite some time on this time, when 
> using 64 bits integers and ctypes on ubuntu edgy. As I know other people 
> use ubuntu with numpy, this may save some headache to others. I found 
> this behaviour which looks like a bug in ctypes for python2.5 on edgy 
> ubuntu:
> 
>     python2.5 -c "from ctypes import sizeof, c_longlong; print 
> sizeof(c_longlong)"
> 
>     prints 4 instead of 8, which in my case is problematic for 
> structures alignement. This affects only python2.5, and does not affect 
> a python installed from sources. Can anybody else reproduce this ?

Can you try a similar program in C compiled with the same C compiler that you
used to build ctypes? sizeof(long long) does not have to be 8 bytes; it just has
to be at least as large as sizeof(long).

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco

Re: [Numpy-discussion] [OT] Can anybody else reproduce this ? (but in ctypes)

[David C. <da...@ar...>]

Robert Kern wrote:
> David Cournapeau wrote:
>   
>> Hi,
>>
>>     This is a bit OT, but I wasted quite some time on this time, when 
>> using 64 bits integers and ctypes on ubuntu edgy. As I know other people 
>> use ubuntu with numpy, this may save some headache to others. I found 
>> this behaviour which looks like a bug in ctypes for python2.5 on edgy 
>> ubuntu:
>>
>>     python2.5 -c "from ctypes import sizeof, c_longlong; print 
>> sizeof(c_longlong)"
>>
>>     prints 4 instead of 8, which in my case is problematic for 
>> structures alignement. This affects only python2.5, and does not affect 
>> a python installed from sources. Can anybody else reproduce this ?
>>     
>
> Can you try a similar program in C compiled with the same C compiler that you
> used to build ctypes? sizeof(long long) does not have to be 8 bytes; it just has
> to be at least as large as sizeof(long).
>
>   
I thought that ISO C99 required long long to be at least 64 bits, and 
that gcc followed this by default:

#include <stdio.h>

int main(void)
{
    printf("size of long long is %d\n", sizeof(long long));
    return 0;
}

compiled by gcc with -W -Wall, returns 8. Gcc is edgy ubuntu, that is 
4.1.2. I tried also with gcc 3.3 and 4.0, same result. Also, something I 
didn't say is that c_int64 is not available from ctypes; with python2.4, 
this is fine  (I changed my code to use c_int64 instead: an import error 
is much easier to find than a structure alignement problem when using 
ctypes :) ).

Also, I insist on this point, installing python from sources returns 8, 
as does python2.4 packaged by ubuntu (which is compiled by the exact 
same compiler according to python prompts). I am now trying to see if 
this is coming from configuration options (now, I know what a dual cpu 
is useful for: compiling python with make -j5 is really fast:) ),

cheers,

David

Re: [Numpy-discussion] [OT] Can anybody else reproduce this ? (but in ctypes)

[David C. <da...@ar...>]

David Cournapeau wrote:
> Robert Kern wrote:
>   
>> David Cournapeau wrote:
>>   
>>     
>>> Hi,
>>>
>>>     This is a bit OT, but I wasted quite some time on this time, when 
>>> using 64 bits integers and ctypes on ubuntu edgy. As I know other people 
>>> use ubuntu with numpy, this may save some headache to others. I found 
>>> this behaviour which looks like a bug in ctypes for python2.5 on edgy 
>>> ubuntu:
>>>
>>>     python2.5 -c "from ctypes import sizeof, c_longlong; print 
>>> sizeof(c_longlong)"
>>>
>>>     prints 4 instead of 8, which in my case is problematic for 
>>> structures alignement. This affects only python2.5, and does not affect 
>>> a python installed from sources. Can anybody else reproduce this ?
>>>     
>>>       
>> Can you try a similar program in C compiled with the same C compiler that you
>> used to build ctypes? sizeof(long long) does not have to be 8 bytes; it just has
>> to be at least as large as sizeof(long).
>>
>>   
>>     
> I thought that ISO C99 required long long to be at least 64 bits, and 
> that gcc followed this by default:
>   
Ok, I found the problem: python 2.5 is configured with the option   
--with-system-ffi. If I compile python2.5 original sources with this 
option, I have the same problem, so it looks like a ffi-related problem. 
I will investigate this, because this is really annoying, but this has 
nothing to do with python nor numpy anymore,

cheers,

David