Re: 64bit access to an array of 8bit values

[Jeffrey Carter <jrcarter@acm.org>]

If you're willing to limit yourself to those machines that actually have
8-bit byte access (which your code would require), you can do

type Bit8 is new Interfaces.Unsigned_8;
-- This won't compile on machines that don't have 8-bit byte access.

type Bit64 is mod 2 ** 64;

type Ram_List is array (Natural range <>) of aliased Bit8;
for Ram_List'Component_Size use Bit8'Size;
pragma Pack (Ram_List);

Bytes_Per_Quad_Word : constant := 8;

subtype Quad_Word_As_Ram_List is Ram_List (1 .. Bytes_Per_Quad_Word);

function To_Quad_Word is new Ada.Unchecked_Conversion
(Source => Quad_Word_As_Ram_List, Target => Bit64);
function To_Ram_List is new Ada.Unchecked_Conversion
(Source => Bit64, Target => Quad_Word_As_Ram_List);

Ram   : Ram_List (0 .. Whatever);
Value : Bit64;
...
Value := To_Quad_Word (Ram (Ram'First .. Ram'First + Bytes_Per_Quad_Word
- 1) );

If you really need to have access values then you should look into
System.Address_To_Access_Conversions, and convert the address of the
first byte of the 64-bit value to the access-to-64-bit-value type.

To be really portable, you need to decide what byte order you want your
64-bit values to have, and do the appropriate conversion on machines
with a different endianness.

-- 
Jeff Carter
"Nobody expects the Spanish Inquisition!"
Monty Python's Flying Circus