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From: Simon Pilgrim <simon.pilgrim@gecm.com>
Subject: Re: Size of 0..255 is not 8 bits?
Date: 1998/05/14
Message-ID: <355B94D0.4812@gecm.com>#1/1
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References: <355A436E.11F76529@cl.cam.ac.uk>
 <matthew_heaney-ya023680001305982154260001@news.ni.net>
 <355AEA1D.6C292667@cl.cam.ac.uk> <dewar.895191407@merv>
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Organization: GEC Marconi Avionics
Newsgroups: comp.lang.ada
Date: 1998-05-14T00:00:00+00:00
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Robert Dewar wrote:
> 
> <<This did not change anything, V is still a 16-bit integer. I get
> no difference whether the 'Size clause is for the type, the object,
> both or none at all. Only
> >>
> 
> It is indeed a bug in a compiler if a Size clause for an object does not
> result in the object tkaing the indicated nnumber of bits. But perhaps
> you had better post the EXACT code that leads you to that conclusion.

After reading one of your posts in another thread on 'size, I took
Markus' code and added some lines to display the sizes:

----------------------------------
   with Ada.Text_IO.Text_Streams, Ada.Text_IO, Ada.Integer_Text_IO;
   use  Ada.Text_IO.Text_Streams, Ada.Text_IO, Ada.Integer_Text_IO;

   procedure Strange2 is
      type ValueType is range 0..255;
      for ValueType'Object_Size use 8;
      V: ValueType;
   begin
      Put ("          ValueType'last:");
      Put (Integer(ValueType'last));
      New_line;
      Put ("          ValueType'size:");
      Put (Integer(ValueType'size));
      New_line;
      Put ("   ValueType'object_size:");
      Put (Integer(ValueType'object_size));
      New_line;
      Put ("                  V'size:");
      Put (Integer(V'size));
      New_line;

      for X in 1..5 loop
         ValueType'Read(Stream(Standard_Input), V);
         Put(Integer(V));
      end loop;
   end Strange2;
----------------------------------

I compiled and ran this with GNAT 3.10p on WinNT4 and got the following:

 >echo ABCDEFGHIJKLMNOP | ./strange2
          ValueType'last:        255
          ValueType'size:          8
   ValueType'object_size:          8
                  V'size:          8
         65         67         69         71         73
This appears to be reading 8 bit chunks from the stream, but every other
byte.

If I changed the range of ValueType to 0..127 and rebuilt, I got the
following:

  >echo ABCDEFGHIJKLMNOP | ./strange2
          ValueType'last:        127
          ValueType'size:          7
   ValueType'object_size:          8
                  V'size:          8
         65         66         67         68         69
This works as I expect.

Regards,

Simon Pilgrim