Checking byte order using unchecked_conversion

Checking byte order using unchecked_conversion

[Steve Scheuber]

I'm posting this for a co-worker.  Please respond via e-mail.
Thank you.
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I would like to know if the following code reliably detects byte order
using Unchecked_Conversion. (I don't have access to a big-endian machine.)
This correctly detected byte order on a DEC VAX using ACS Ada.

with System,
     Text_IO,
     Unchecked_Conversion;

procedure Byte_Order is
    Byte      : constant := System.Storage_Unit;
    Short_Int : constant := 2*Byte;

    type Bit8 is range 0 .. 2**Byte - 1;
    for Bit8'Size use Byte;

    type Bit16 is range 0 .. 2**Short_Int - 1;
    for Bit16'Size use Short_Int;

    type Bit16_Array is array(1..2) of Bit8;
    for Bit16_Array'Size use Short_Int;

    function Map is new Unchecked_Conversion(Source => Bit16,
                                             Target => Bit16_Array);

    The_Bit16    : constant Bit16 := 1;
    Mapped_Bit16 : constant Bit16_Array := Map(The_Bit16);

begin

    if Mapped_Bit16'First = 1 then
        Text_IO.Put_Line("Low byte order");
    elsif 
        Text_IO.Put_Line("High byte order");
    end if;
end Byte_Order;
-- 
Steve Scheuber                       NCYC Lives!
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