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: f849b,b8d52151b7b306d2
X-Google-Attributes: gidf849b,public
X-Google-Thread: 103376,a00006d3c4735d70
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-12-30 07:12:29 PST
Path: 
 archiver1.google.com!news2.google.com!fu-berlin.de!uni-berlin.de!mail.nartron.COM!not-for-mail
From: iddw@hotmail.com (Dave Hansen)
Newsgroups: comp.arch.embedded,comp.lang.ada
Subject: Re: Certified C compilers for safety-critical embedded systems
Date: Tue, 30 Dec 2003 14:48:19 GMT
Message-ID: <3ff18d4d.603356952@News.CIS.DFN.DE>
References: <3fe00b82.90228601@News.CIS.DFN.DE> <3FE026A8.3CD6A3A@yahoo.com>
 <x0%Db.16$_l6.25998@news.uswest.net>
 <3bf1uvg2ntadvahfud2rg6ujk24sora6gr@4ax.com>
 <2u3auvogde8ktotlaq0ldiaska3g416gus@4ax.com> <bs62ph$giu$1@newshost.mot.com>
 <20619edc.0312221020.3fd1b4ee@posting.google.com>
 <b5feuv06s2nmpakq0o1b7v0kpd450v3eli@4ax.com>
 <20619edc.0312222106.3b369547@posting.google.com>
 <45cs9hAbLc6$EAAx@phaedsys.demon.co.uk> <3fe9f0d7.104475725@News.CIS.DFN.DE>
 <FaLTFYBFof6$EAVI@phaedsys.demon.co.uk>
 <5802069.JsgInS3tXa@linux1.krischik.com>
 <1072464162.325936@master.nyc.kbcfp.com>
 <1563361.SfB03k3vvC@linux1.krischik.com>
 <11LvOkBBXw7$EAJw@phaedsys.demon.co.uk> <3ff0687f.528387944@News.CIS.DFN.DE>
 <1086072.fFeiH4ICbz@linux1.krischik.com>
NNTP-Posting-Host: mail.nartron.com (216.65.187.224)
X-Trace: news.uni-berlin.de 1072795462 869188 216.65.187.224 ([97677])
X-Newsreader: Forte Free Agent 1.21/32.243
Xref: archiver1.google.com comp.arch.embedded:6349 comp.lang.ada:3947
Date: 2003-12-30T14:48:19+00:00
List-Id: <comp.lang.ada>

On Tue, 30 Dec 2003 11:18:55 +0100, Martin Krischik
<krischik@users.sourceforge.net> wrote:

>Dave Hansen wrote:
[...re: plain, signed, and unsigned char...]
>> All three are integer types.  All three are 1 byte wide ("byte" does
>> not mean "8 bits").
>
>That is why Ada 'Size gives you the size in bits. No misunderstanding here. 

In C, CHAR_BIT gives you the number of bits in [[un]signed] char.  It
must be >= 8.

>
>>>>If you are lucky you have real C99 compiler with byte.
>> 
>> I'm not sure what you mean.  There's no such thing as "byte."
>> uint8_t?  Not guaranteed to exist.  unint_least8_t?  That would work,
>> but I fear relatively few even know it exists, let alone how to use
>> it...
>
>You allwas learn something new. But unint_least8_t is not helpfull for
>safety-critical embedded systems. You might need exaclty 8 bit.

If a platform supports uint8_t (unsigned integer exactly 8 bits wide)
the compiler must provide the type.  If the platform does not support
the type, you have to choose another platform.

>
>Which brings me back to the original Question. How will you do this in C:
>
>type Month is new Integer range 1 .. 12;
>for Month'Size is 8;

You could do something like

   typedef struct month{
      value:8;
   } Month;

>
>Or even better:
>
>type Display_Element is Interger range 0 .. 9;
>for Display_Element'Size use 4;

   typedef struct display_element{
      value:4;
   } Display_Element;

>
>type Display_Array is array (Integer range 1 .. 6) of Display_Element;
>pragma Pack (Display_Array);

   typedef struct display_array{
      elt0: 4;
      elt1: 4;
      elt2: 4;
      elt3: 4;
      elt4: 4;
      elt5: 4;
   } Display_Array;

>
>Display : Display_Array;
>for Display'Address use 16#12_3456#;

   Display_Array *Display = (Display_Array *) 0x123456;

Though in no case would the ranges be enforced.  Heck, enumerations
aren't enforced in any way either:

   enum { Red, Green, Blue } color;
   int number;

   color = 42;
   number = Red;

Is perfectly fine as far as the compiler is concerned.

>We are talking "safety-critical embedded systems". The Plane might crash if
>11 is ever stored in a Display_Element.

Then don't do that.  ;-)

Regards,

                               -=Dave
-- 
Change is inevitable, progress is not.