[M3devel] I know, I know...

[Tony Hosking]

PACKED?

Sent from my iPad

On Aug 23, 2012, at 3:24 AM, Dragiša Durić <dragisha at m3w.org> wrote:

> I know this will probably be very dense subject, but… What about:
> 
>  TSPacketHeader = <* ENDIAN = BIG*>RECORD
>    sync: BITS 8 FOR [16_0..16_ff];   (* Always 0x47 *)
>    tErrInd,                      (* Transport Error Indicator *)
>    pusi: BITS 1 FOR BOOLEAN;     (* Payload Unit Start Indicator *)
>    transPrio: BITS 1 FOR [0..1];
>    pid: BITS 13 FOR PID;
>    transScramControl: BITS 2 FOR [0..3]; (* 00 means no scrambling *)
>    afc: BITS 2 FOR [0..3]; (* 01 - no adaptation field, payload only *) 
>    cc: BITS 4 FOR Nibble;
>  END;
> 
> Meaning: bit data is packed from left to right, and all multi-byte data is packed MSB first.
> 
> Right now I am doing this, based on knowledge of my platform (little endian, x86_64), like this:
> 
>  TSPacketHeader = RECORD
>    sync: BITS 8 FOR [16_0..16_ff];   (* Always 0x47 *)
> 
>    pidHi: BITS 5 FOR [16_00..16_1f];
>    transPrio: BITS 1 FOR [0..1];
>    pusi,
>    tErrInd: BITS 1 FOR BOOLEAN;
> 
>    pidLo: BITS 8 FOR [16_00..16_ff];
> 
>    cc: BITS 4 FOR Nibble;
>    afc: BITS 2 FOR [0..3]; (* 01 - no adaptation field, payload only *) 
>    transScramControl: BITS 2 FOR [0..3]; (* 00 means no scrambling *)
>  END;
> 
> And please don't tell me "write in C", because then I will just "offload" this problem to C preprocessor and still only hope for the best. Modula-3 is provably very adept to systems programming and I hope it can be more so.
> 
> Thanks in advance..
> --
> Divided by a common language
> 
> Dragiša Durić
> dragisha at m3w.org
> 
> 
> 
>