Re: Translating an embedded C algorithm

[Cesar Rabak <csrabak@yahoo.com.br>]

Niklas Holsti escreveu:
> Niklas Holsti wrote:
>> ...
>>
>> I agree with other posters that simply translating this function into 
>> Ada does not give a good comparison between C and Ada. The first steps 
>> in an Ada design would be to consider encapsulation (packages) and 
>> data representation (types), for which the C version gives no model.
> 
> I'm replying to my own post because I've changed my opinion a bit: I 
> think that an Ada translation of this C function can, with a bit of 
> elaboration, illustrate several Ada features for "programming in the 
> small", even if not for "programming in the large".
> 
> So here is my try at an Ada version of the code and some of the context. 
> This makes for a long post, for which I apologize in advance. Putting 
> the sources somewhere for download seemed like overkill, and I prefer to 
> expose my suggestion to the purifying flames of c.l.a instead of sending 
> it privately to the OP. The Ada code below has been compiled
> and tested (gnat 3.15p, Debian). It is hereby put in the public domain.

Nice! I will only make a pair of comments that I believe relate to the 
OP idea, and will skip suggestions or observations which in the bottom 
line may be considered by other engineers as stylistic.

> 
> In this code, I tried to use as many relevant Ada features as possible, 
> without trying to limit myself to some "8-bit subset". It would be 
> interesting to compile this code with AVR-Ada; I don't happen to have 
> that installed, but I may try it later, if no-one else does it.

Note that the home page for AVR-Ada has this (Status 2nd paragraph):


"The Ada run time system (RTS) on the other hand is for the most part 
not even a run time system. It is more a compile time system :-). Most 
files in the RTS are only needed at compile time. As a consequence we 
don't yet have support for exceptions nor for tasking (multi-threading)."



[snipped]

> and
> 
>    package Temperatures is
> 
>       type Celsius_T is delta 0.1 digits 5 range -40.0 .. 120.0;
>       --
>       -- A temperature in degrees Celsius.
> 
>       -- More temperature stuff ...
> 
>    end Temperatures;

I don't know how an Ada compiler targeted for microcontrollers would 
make the internal representation of this type, but if it employs more 
than a 16 bit word, I would rather stick to the other implementation 
elsethread.

[snipped]

HTH

--
Cesar Rabak