[fpc-pascal] Implementation of variant records

[Sven Barth]

Am 07.07.2019 um 02:55 schrieb Ralf Quint:
> On 7/6/2019 12:21 PM, Florian Klaempfl wrote:
>> Am 05.07.2019 um 13:53 schrieb Ralf Quint:
>>> Shouldn't a PACKED Record guarantee that values are aligned at the byte
>>> level?
>> It does in TP, but the ISO says only that it shall be economised.
>>
> Well, the ISO is probably what has done most of the damage to Pascal. 
> AFAIK, the ISO doesn't not actually specify any "packed record" per 
> se, but there is an explicit PACK and UNPACK procedures to more 
> economically store sets and arrays (and possibly records, I would have 
> to look up the ISO text to be certain). For example this would be 
> something to create bit fields, pretty much the only feature of C that 
> I sometimes miss in (Free)Pascal.
You mean like this?

=== code begin ===

struct Test
{
         uint8_t field1;
         uint16_t bfield1 : 1;
         uint16_t bfield2 : 1;
         uint16_t bfield3 : 3;
         uint16_t bfield4 : 5;
         uint16_t bfield5 : 1;
         uint16_t field2;
};

=== code end ===

=== code begin ===

type
   TTest = bitpacked record
     field1: UInt8;
     bfield1: 0..1;
     bfield2: 0..1;
     bfield3: 0..7;
     bfield4: 0..31;
     bfield5: 0..1;
     pad: UInt8; // needed due to bitpacked
     field2: UInt16;
   end;

=== code end ===

The size of both records is 6. :)

Regards,
Sven