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From: Alan E & Carmel J Brain <aebrain@dynamite.com.au>
Subject: Re: Beware: Rep spec on an enumeration type causes code explosion
Date: 1997/12/14
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Date: 1997-12-14T00:00:00+00:00
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Rakesh Malhotra wrote:

> We work on safety critical projects.  And if we have a safety critical
> bit of code that defines and uses an enumeration then we use the rep
> clause to provide more than 1 bit separation between adjacent values in
> the enumeration.  That way if 1 bit got corrupted the value could not
> become some other legal value.

See if I understand you correctly: Thus you'd use 2#1100 and 2#0011 for
example, to avoid single-bit soft failures. Just don't choose 2#0000 and
2#1111 as many soft failures either latch high or latch low. Right?

Interesting, not seen this technique used before, but it makes sense in
some areas. And my vast ignorance is infinitesimally decreased,
thank-you.

Am I right in thinking that in the areas where such paranoia is
reasonable, the code could well look like:

SECTION_1
begin
  single statement, or at most a few
exception
  when (etc)
end SECTION_1;

SECTION_2
begin
  single statement, etc
exception
  when (etc)
end SECTION_2;

and repeat as nauseum.

Such code, where efficiency is not a major consideration :) might well
be appropriate in certain specialised areas. Just not in the general
case, even for safety-critical stuff.
-- 
aebrain@dynamite.com.au     <> <>    How doth the little Crocodile
| Alan & Carmel Brain|      xxxxx       Improve his shining tail?
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