[fpc-pascal] does the following translation of a c struct to FPC is correct ?

[ik]

On Sun, Feb 26, 2012 at 15:08, Jonas Maebe <jonas.maebe at elis.ugent.be> wrote:
>
> On 26 Feb 2012, at 13:54, ik wrote:
>
>> to the following Pascal record:
>>
>>
>> iphdr    = record
>> {$IFDEF ENDIAN_LITTLE}
>>              jhl     : Cardinal; // __u8      ihl:4,
>>              version : Cardinal; // version:4
>
> The ":4" in C means "4 bits", not 4 bytes. The correct translation in the general case for bitfields is hard, because FPC does not support C-compatible bitpacking (it depends on the type of the bitfield, e.g. "int a:4;" and "char a:4" have different alignment rules). In this case, this should match the C layout:
>
> {$packrecords c}
> iphdr    = record
>             bitfields = bitpacked record
> {$IFDEF ENDIAN_LITTLE}
>               jhl: 0..(1 shl 4)-1;
>               version: 0..(1 shl 4)-1;
> {$ELSE}
>               jhl: 0..(1 shl 4)-1;
>               version: 0..(1 shl 4)-1;
> {$ENDIF}
>             end;
>             tos      : cuint8;
>             tot_len  : cint16;
>             id       : cint16;
>             frag_off : cint16;
>             ttl      : cint8;
>             protocol : cint8;
>             check    : cuint16;
>             saddr    : cint32;
>             daddr    : cint32;
>  end;
>
> You will then of course have to use iphdrvar.bitfields.jhl instead of iphdrvar.jhl.

I'ved replaced it to

iphdr    = bitpacked record
{$IFDEF ENDIAN_LITTLE}
              jhl     : 0..(1 shl 4)-1; // __u8	ihl:4,
              version : 0..(1 shl 4)-1; // version:4
{$ELSE}
              version : 0..(1 shl 4)-1; // __u8 version:4,
              jhl     : 0..(1 shl 4)-1; // version:4
{$ENDIF}
              tos      : cuint8;
              tot_len  : cint16;
              id       : cint16;
              frag_off : cint16;
              ttl      : cint8;
              protocol : cint8;
              check    : cuint16;
              saddr    : cint32;
              daddr    : cint32;
  end;

And now all of the problems that I continue to find gone away.

Thank you

>
>
> Jonas_______________________________________________
> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
> http://lists.freepascal.org/mailman/listinfo/fpc-pascal