Re: Bit manipulation

[Martin Krischik <martin@krischik.com>]

Maurizio wrote:

> hi, i need two hint:
> 
> i need to acces to a 32 bit word (Interfaces.Unsigned_32).
> how i can do to take the three m.s.bit? (30,31,32)

Have you considered using a packed array?

http://en.wikibooks.org/wiki/Programming:Ada:Types:array#with_aliased_elements

Prehaps on conjunction with Unchecked_Conversion. 

> second, i need to send the 32 bit word over a Tcp connection to a C
> program, but
> socket work with usigned 8 bit word, so i need to split the 32 bit in
> 4 8bit word,
> and when i read from the socket take 4 8bit word and combine in a 32
> word.
> 
> i see that Ada.Unchecked_Conversion work (in an ada client/server test
> program)  but is correct?
> 
> --com_buffer_type is an array of  128 32bit word
> 
> subtype Datas is Ada.Streams.Stream_Element_Array(1..512); --128*4

Stream Elements are normaly not used directly. Ada.Streams only provide a
framework for the 'Read, 'Write, 'Input, and 'Output attributes. If you
know Java: It works a bit like the Serializable interface.

'Read, 'Write are low level - reading and writing raw data.
'Input, and 'Output are high level - storing array bound, object type etc.
pp. as well.

> function To_Raw is
>    new Ada.Unchecked_Conversion
>       (
>       Source => Com_Buffer_Type,  --Interfaces.Unsigned_32
>       Target => Datas);     --Stream_Element is mod 2 **
> Standard'Storage_Unit
>    function From_Raw is
>    new Ada.Unchecked_Conversion
>       (
>       Source => Datas,
>       Target => Com_Buffer_Type);

You should give com_buffer_type'Write (Stream, Datas)  a try.

Martin
-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com