Re: Adding offset to 'Address

[Kim Rostgaard Christensen <krc@greenpc.dk>]

tmoran@acm.org wrote:
>>  Raw_Bytes : access Unsigned_Char
>>  for Ethernet_Header'Address use Raw_Bytes.all'Address;
>>
>> and additionally need something like:
>>  for IP_Packet'Address use Raw_Bytes.all'Address + Ethernet_Header'Size;
> 
> It's not clear to me exactly what problem you are trying to get past.

The problem was basically to perform arithmethics on system addresses

> How about something like:
> 
> with Ada.Unchecked_Conversion,
>      Interfaces.C;
> procedure Eiptest is
>   type Ethernet_Header_Type is new Integer;          -- or whatever
>   type IP_Packet_Type is array (1 .. 5) of Integer;  -- "
> 
>   type R_Type is record
>     Ethernet_Header: Ethernet_Header_Type;
>     IP_Packet: IP_Packet_Type;
>     Other_Stuff : Integer;
>   end record;
>   for R_Type use record
>     Ethernet_Header at 0 range 0 .. 31;
>     IP_Packet at 4 range 0 .. 159;
>     Other_Stuff at 30 range 0 .. 31;
>   end record;
> 
>   type Lpvoid is access all Interfaces.C.Char;
>   type R_Ptr_Type is access all R_Type;
> 
>   function Convert is new Ada.Unchecked_Conversion
>     (Source => Lpvoid, Target => R_Ptr_Type);
> 
>   procedure Process(Raw_Bytes: in Lpvoid) is
>     R_Ptr   : constant R_Ptr_Type := Convert(Raw_Bytes);
>     This_IP_Packet: IP_Packet_Type renames R_Ptr.IP_Packet;
>   begin
>     null; -- do something with This_IP_Packet
>   end Process;
> 
>   Buffer : Interfaces.C.Char_Array(1 .. 100);
> 
> begin
>   Process(Buffer(1)'access);
> end Eiptest;

This is a nice approch, I will try it out.

- Kim