AW: Translating an embedded C algorithm

AW: Translating an embedded C algorithm

[Grein, Christoph (Fa. ESG)]

No, there are again some mistakes:

...
> --| Temperature in ºC x 10. INVALID_TEMPERATURE if out of range.

Incorrect: There's no INVALID_TEMPERATURE

...
>   InterpolationDistance := (Adc_Count - MINIMUM_ADC_COUNT) mod (SPACING - 1);

Wrong again: mod Spacing

But: As others have pointed out, a mere translation of C code is not Ada. You would use constrained types rather than Integer and other Ada idioms (put it in a package, add context clauses, use different integer types for different abstractions etc...).

Re: AW: Translating an embedded C algorithm

[Ludovic Brenta]

Grein, Christoph (Fa. ESG) writes:
> No, there are again some mistakes:
>
> ...
>> --| Temperature in ºC x 10. INVALID_TEMPERATURE if out of range.
>
> Incorrect: There's no INVALID_TEMPERATURE
>
> ...
>>   InterpolationDistance := (Adc_Count - MINIMUM_ADC_COUNT) mod (SPACING - 1);
>
> Wrong again: mod Spacing
>
> But: As others have pointed out, a mere translation of C code is not
> Ada. You would use constrained types rather than Integer and other
> Ada idioms (put it in a package, add context clauses, use different
> integer types for different abstractions etc...).

Right, and there would be no need for a silly INVALID_TEMPERATURE.
What *is* an invalid temperature anyway?  One that needs crutches?
One that is excused from military service? And why would you ever
return an invalid temperature to your caller? etc. etc.

-- 
Ludovic Brenta.

Re: AW: Translating an embedded C algorithm

[Markus E Leypold]

Ludovic Brenta <ludovic@ludovic-brenta.org> writes:

> Grein, Christoph (Fa. ESG) writes:
>> No, there are again some mistakes:
>>
>> ...
>>> --| Temperature in �C x 10. INVALID_TEMPERATURE if out of range.
>>
>> Incorrect: There's no INVALID_TEMPERATURE
>>
>> ...
>>>   InterpolationDistance := (Adc_Count - MINIMUM_ADC_COUNT) mod (SPACING - 1);
>>
>> Wrong again: mod Spacing
>>
>> But: As others have pointed out, a mere translation of C code is not
>> Ada. You would use constrained types rather than Integer and other
>> Ada idioms (put it in a package, add context clauses, use different
>> integer types for different abstractions etc...).
>
> Right, and there would be no need for a silly INVALID_TEMPERATURE.
> What *is* an invalid temperature anyway?  One that needs crutches?
> One that is excused from military service? And why would you ever
> return an invalid temperature to your caller? etc. etc.


| >> --| Temperature in �C x 10. INVALID_TEMPERATURE if out of range.

If the sensor is out of order or the temperature leaves the range
where it functions properly?

:-). 

Regards -- Markus

Re: AW: Translating an embedded C algorithm

[Ludovic Brenta]

Markus E Leypold writes:
> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
>> Right, and there would be no need for a silly INVALID_TEMPERATURE.
>> What *is* an invalid temperature anyway?  One that needs crutches?
>> One that is excused from military service? And why would you ever
>> return an invalid temperature to your caller? etc. etc.
>
> | >> --| Temperature in ºC x 10. INVALID_TEMPERATURE if out of range.
>
> If the sensor is out of order or the temperature leaves the range
> where it functions properly?
>
> :-). 

My point it this: if the sensor is out of order, then there is no
known temperature; not a known "invalid" temperature.  The proper way
to handle that in Ada is with an exception, not a special value of
type Degrees_C.

-- 
Ludovic Brenta.

Re: AW: Translating an embedded C algorithm

[Markus E Leypold]

Ludovic Brenta <ludovic@ludovic-brenta.org> writes:

> Markus E Leypold writes:
>> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
>>> Right, and there would be no need for a silly INVALID_TEMPERATURE.
>>> What *is* an invalid temperature anyway?  One that needs crutches?
>>> One that is excused from military service? And why would you ever
>>> return an invalid temperature to your caller? etc. etc.
>>
>> | >> --| Temperature in �C x 10. INVALID_TEMPERATURE if out of range.
>>
>> If the sensor is out of order or the temperature leaves the range
>> where it functions properly?
>>
>> :-). 
>
> My point it this: if the sensor is out of order, then there is no
> known temperature; not a known "invalid" temperature.  The proper way

Yep, certainly. Actually 'temperature' is the wrong description for
this type. It's actually "the result of reading the temperature
sensor" which is a union type between a finite temperature range and
the "invalid result".

> to handle that in Ada is with an exception, 

That depends on how "exceptional" that event is. If it is a hardware
failure an exception would perhaps be better, but if it just means
"temperature went out of range" (or better "too high") dependend on
what kind of apparatus we have here, it might be better to handle that
as a special case (like: a very high temperature we don't don't knoe
exactly). A (very primitive and perhaps incomplete) example: A
temperature sensor for some kind of nuclear or chemical process. If
the the temperature becomes > t2 we'd want the emergency cooling to be
activated. We'd also want this if the it becomes > t3, the temperature
where the sensor stops to work properly (which is higher than t2, but
where we still know that the temperature is too high). In that case an
exception or even an emergency shutdown of the controlling unit would
be wrong.

> not a special value of type Degrees_C.

Agreed. Degrees_C is misleading. What about Sensor_Result?

Regards -- Markus

Re: AW: Translating an embedded C algorithm

[Stephen Leake]

Ludovic Brenta <ludovic@ludovic-brenta.org> writes:

> Markus E Leypold writes:
>> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
>>> Right, and there would be no need for a silly INVALID_TEMPERATURE.
>>> What *is* an invalid temperature anyway?  One that needs crutches?
>>> One that is excused from military service? And why would you ever
>>> return an invalid temperature to your caller? etc. etc.
>>
>> | >> --| Temperature in �C x 10. INVALID_TEMPERATURE if out of range.
>>
>> If the sensor is out of order or the temperature leaves the range
>> where it functions properly?
>>
>> :-). 
>
> My point it this: if the sensor is out of order, then there is no
> known temperature; not a known "invalid" temperature.  The proper way
> to handle that in Ada is with an exception, not a special value of
> type Degrees_C.

In a real-time system that is tolerant of hardware failures, every
hardware measurement should be accompanied by some sort of quality
flag. In this case, a boolean would do; Temperature_Valid.

The point is that when hardware failures are expected, they are best
handled by normal data, not exceptions.

Using a special value of Temperature to represent hardware failure is
an example of in-band signaling; using a separate quality flag is
out-of-band signaling. Out-of-band is a bit more complicated, but
much more robust.


This example program is far too small to show the crucial differences
between C and Ada.

-- 
-- Stephe

Re: AW: Translating an embedded C algorithm

[Cesar Rabak]

Stephen Leake escreveu:
> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
[snipped]
> 
> This example program is far too small to show the crucial differences
> between C and Ada.
> 

I think you summarized very well the whole issue here!

Re: AW: Translating an embedded C algorithm

[Robert A Duff]

Cesar Rabak <csrabak@yahoo.com.br> writes:

> Stephen Leake escreveu:
>> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
> [snipped]
>> This example program is far too small to show the crucial differences
>> between C and Ada.
>>
>
> I think you summarized very well the whole issue here!

But the OP didn't ask anybody to "show the crucial differences between C
and Ada"; he asked for a simple half-page C function to be translated
into Ada, which is a perfectly reasonable request.  I started to do it
myself, but others have answered that question, so he got more-or-less
what he asked for.  He also got "we can't translate simple C into simple
Ada -- we need to create a hugely complicated mess", and he also got
"you dope, how dare you ask about Ada when you don't already know Ada".
Sigh.

- Bob

Re: AW: Translating an embedded C algorithm

[Cesar Rabak]

Robert A Duff escreveu:
> Cesar Rabak <csrabak@yahoo.com.br> writes:
> 
>> Stephen Leake escreveu:
>>> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
>> [snipped]
>>> This example program is far too small to show the crucial differences
>>> between C and Ada.
>>>
>> I think you summarized very well the whole issue here!
> 
> But the OP didn't ask anybody to "show the crucial differences between C
> and Ada"; he asked for a simple half-page C function to be translated
> into Ada, which is a perfectly reasonable request. 

Yes.

> I started to do it
> myself, but others have answered that question, so he got more-or-less
> what he asked for. 

OK. I believe he got a handful set of examples.

> He also got "we can't translate simple C into simple
> Ada -- we need to create a hugely complicated mess", and he also got
> "you dope, how dare you ask about Ada when you don't already know Ada".

While I have to agree that hearing from the aisles our internal 
discussion could be described like that, I think we have to think about 
the other side.

A direct translation of a that half page (C language) function, would 
convey very little about Ada, and perhaps lead to a conclusion that is 
just a C (or rather Pascal) like language with a "weird syntax" (pundits 
could step and say all other things we're used, as being verbose, etc.).

So a reasonable (I agree that with less ado) remark that Ada language to 
be used in its full potential would include more code (like was shown in 
the thread already) and a clear and better explanation of the advantages 
of it would have been better advertising of Ada.


> Sigh.

Relieved? :-)

Re: Translating an embedded C algorithm

[Dmitry A. Kazakov]

On Fri, 19 Jan 2007 15:27:58 -0500, Robert A Duff wrote:

> But the OP didn't ask anybody to "show the crucial differences between C
> and Ada"; he asked for a simple half-page C function to be translated
> into Ada, which is a perfectly reasonable request.

Sure, but that piece of code was intended to demonstrate a solution of some
problem by means of a programming language.

> He also got "we can't translate simple C into simple
> Ada -- we need to create a hugely complicated mess",

For good or bad, but this one of key features of Ada as a programming
language, I think.

My theory is that Ada has a much finer and precise definition of program
semantics. It is a deeply layered "mess" of "what-ifs," which normal C
programmers would just promptly ignore. In Ada I never know if there
couldn't be a better way, or whether there were a hidden gotcha in some
rare obscure pathological case. This is not good. In C++ I just don't care,
I know for sure, there are lots. My attitude is different. This is also not
good, but has huge psychological (=>marketing) advantages over Ada.

> and he also got
> "you dope, how dare you ask about Ada when you don't already know Ada".

I don't justify this, but I understand the reasons, cultural reasons. I
tolerate much worse C++ code from myself and others, than I could in the
case of an "equivalent" Ada code.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: AW: Translating an embedded C algorithm

[Jeffrey Carter]

Robert A Duff wrote:
> "you dope, how dare you ask about Ada when you don't already know Ada".

No. He got, "Are you qualified to write a book on real-time embedded SW 
development when you only know C?"

Re: AW: Translating an embedded C algorithm

[Robert A Duff]

Jeffrey Carter <spam.jrcarter.not@spam.acm.not.org> writes:

> Robert A Duff wrote:
>> "you dope, how dare you ask about Ada when you don't already know Ada".
>
> No. He got, "Are you qualified to write a book on real-time embedded SW
> development when you only know C?"

OK, I admit it -- I exaggerated a little.  ;-)

Still, IMHO a gentler approach would be more likely to get him to (1)
learn something about Ada and/or (2) put a small Ada example in his
book, thus tempting others to learn about it.

I'm sure you didn't mean to attack the guy, but questioning someones
competence could come across that way, don't you think?

- Bob

Re: AW: Translating an embedded C algorithm

[Jeffrey Carter]

Robert A Duff wrote:
> 
> I'm sure you didn't mean to attack the guy, but questioning someones
> competence could come across that way, don't you think?

I'm not a very good judge of such things. Obviously a lot of people 
thought so.

In my experience, the vast majority of people involved in SW development 
are not qualified to design SW, much less write books about it. I'm 
marginally qualified, and I'm familiar with a number of people who are 
better qualified, but I'm also familiar with large numbers of people who 
aren't qualified. I think it's very important to SW and the world that 
this situation be improved, so I tend to bring it up when it seems 
important.

I'm not sure what this has to do with my lack of social skills.

Re: AW: Translating an embedded C algorithm

[Stephen Leake]

Jeffrey Carter <spam.jrcarter.not@spam.acm.not.org> writes:

> Robert A Duff wrote:
>> I'm sure you didn't mean to attack the guy, but questioning someones
>> competence could come across that way, don't you think?
>
> I'm not a very good judge of such things. Obviously a lot of people
> thought so.
>
> In my experience, the vast majority of people involved in SW
> development are not qualified to design SW, much less write books
> about it. I'm marginally qualified, and I'm familiar with a number of
> people who are better qualified, but I'm also familiar with large
> numbers of people who aren't qualified. I think it's very important to
> SW and the world that this situation be improved, so I tend to bring
> it up when it seems important.
>
> I'm not sure what this has to do with my lack of social skills.

Since he is _already_ writing a book, clearly he believes he's
qualified. So a statement "you are not qualified" will simply
be rejected.

As I recall, your statement was phrased as a question, something like
"how can you think you are qualified when you don't know Ada". That
implies both that he _isn't_ qualified, and that he doesn't know what
_qualified_ means in the first place. Both messages will simply be
rejected; he will assume you are just a crank, since you don't know
him personally.

Criticizing people effectively is a social skill. I'm a blue-blood
physics nerd, but a few things have rubbed off on me from my
social-worker wife :). Generally, criticism at this level will only be
accepted from someone you know, or someone you have a formal
relationship with; an editor, or an official reviewer.

-- 
-- Stephe

Re: AW: Translating an embedded C algorithm

[Jeffrey R. Carter]

Stephen Leake wrote:
> 
> As I recall, your statement was phrased as a question, something like
> "how can you think you are qualified when you don't know Ada". That
> implies both that he _isn't_ qualified, and that he doesn't know what
> _qualified_ means in the first place. Both messages will simply be
> rejected; he will assume you are just a crank, since you don't know
> him personally.

Actually, it was a statement about myself, along the lines of "I wonder 
if someone who only knows C is qualified."

Re: AW: Translating an embedded C algorithm

[Niklas Holsti]

Dennis Lee Bieber wrote:
> On Wed, 17 Jan 2007 11:26:32 +0100, Ludovic Brenta
> <ludovic@ludovic-brenta.org> declaimed the following in comp.lang.ada:
> 
> 
>>Right, and there would be no need for a silly INVALID_TEMPERATURE.
>>What *is* an invalid temperature anyway?  One that needs crutches?
> 
> 
> 	Well... anything that comes out as less than 0deg Kelvin <G>

Maybe not -- see, for example, 
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/neg_temperature.html

<quote>

Questions: What is negative temperature?  Can you really make a system 
which has a temperature below absolute zero?  Can you even give any 
useful meaning to the expression 'negative absolute temperature'?

Answer: Absolutely. :-)

Under certain conditions, a closed system can be described by a negative 
temperature, and, surprisingly, be hotter than the same system at any 
positive temperature.  This article describes how it all works.

</quote>


-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .