[M3devel] I know, I know...

[Dragiša Durić]

packing, order, alignment. 

--
Divided by a common language

Dragiša Durić
dragisha at m3w.org




On Aug 23, 2012, at 3:30 PM, Tony Hosking wrote:

> 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
>> 
>> 
>> 
>> 

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