[sane-devel] Re: dc240 only works with GCC

[abel deuring]

Peter Fales wrote:
> I've made this change.  I don't see any easy way to fix it
> in portable way, and more importantly I don't have any way to 
> test it.   I'll be glad to take patches if someone wants to supply
> them.
> 
>
> On Fri, Oct 11, 2002 at 06:50:14PM +0200, Petter Reinholdtsen wrote:
> 
>> 
>> I just discovered this code when trying to find out why the CVS
>> version of sane-backends fail to compile on HP/UX using the native
>> compiler.
>> 
>>   #ifdef __GNUC__
>>   #define UNUSEDARG __attribute__ ((unused))
>>   #define PACKED    __attribute__ ((packed))
>>   #else
>>   #define UNUSEDARG
>>   /* You need to figure out a way to ensure that there are no holes
>>    * in the following dir_buf structure - it has to match data read from
>>    * the camera.  gcc does this with __attribute__ ((packed))
>>    */
>>   #error
>>   #endif
>> 
>> 

Well, perhaps I don't get the point -- but looking through dc240.h, it 
seems to me that all you want to achieve is that struct dir_buf does not 
have any padding bytes between members of the struct.

All the SCSI backends have to deal with the same problem for SCSI 
command and data buffers: you may have non-32-bit-aligned 32 bit 
integers, and the integers are perhaps not in the "native" byte order of 
the machine.

Regading struct dir_buf, what about the following (written without a 
serious look into dc240.c -- please bear with me, if I'm writing 
nonsense...):

#define CAMDIRENTRYSIZE 20
#define DIRENTRIES 1000

SANE_Byte dir_buf[2 + CAMDIRENTRYSIZE * DIRENTRIES];

#define get_name(entry) (SANE_Char*) &dir_buf[4+CAMDIRENTRYSIZE*(entry)]
#define get_attr(entry) dir_buf[4+11+CAMDIRENTRYSIZE*(entry)]
#define get_create_time(entry) \
    (  dir_buf[4+12+CAMDIRENTRYSIZE*(entry)] << 8 \
     + dir_buf[4+13+CAMDIRENTRYSIZE*(entry)])


Abel