From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=ham autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,ea4b92bb88a43e50,start
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2001-06-23 03:15:23 PST
Path: 
 archiver1.google.com!newsfeed.google.com!postnews1.google.com!not-for-mail
From: karlran1234@yahoo.com (Karl Ran)
Newsgroups: comp.lang.ada
Subject: Ada records and byte order
Date: 23 Jun 2001 03:15:23 -0700
Organization: http://groups.google.com/
Message-ID: <e7ebd224.0106230215.3f684ac6@posting.google.com>
NNTP-Posting-Host: 217.49.112.51
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
X-Trace: posting.google.com 993291323 11582 127.0.0.1 (23 Jun 2001 10:15:23
 GMT)
X-Complaints-To: groups-support@google.com
NNTP-Posting-Date: 23 Jun 2001 10:15:23 GMT
Xref: archiver1.google.com comp.lang.ada:9054
Date: 2001-06-23T10:15:23+00:00
List-Id: <comp.lang.ada>

Hi there,

I've a question about Ada records:

I have to read a binary file from disk which was written by another program.

The record size is fixed: 3 bytes
The file structure looks like this:
      

|byte 1 | |byte 2 | |byte 3 |   |byte 4...
aaaa.aaaa.bbbb.bbbb.bbbb.cccc | aaaa.a.....
M       L M            L M  L
S       S S            S S  S
B       B B            B B  B

a:  8 bits
b: 12 bits
c:  4 bits

Here is the code ...

procedure test is

   subtype BYTE     is Integer range 0 .. 2 **   8 - 1;
   subtype WORD12   is integer range 0 .. 2 **  12 - 1;
   subtype WORD4    is integer range 0 .. 2 **   4 - 1;

   type My_rec is
      record
         A : BYTE;
         B : WORD12;
         C : WORD4;
      end record;
   
   for My_rec use
      record
         A at 0 range 0 ..  7;
         B at 1 range 0 .. 11;
         C at 2 range 0 ..  3;
      end record;   

   Abc : My_Rec; 

begin
   Abc.b := 16#123#;
   ...
end test;
   
... which fails to compile whith GNAT on a (low-endian) i386:
test.adb:31:10: component "C" overlaps "B" at line 30
         
Is there an Ada like (TM) solution for this kind of (byte order) problem?

   
Thanks,
Karl