Re: Translating an embedded C algorithm

[Niklas Holsti <niklas.holsti@nospam.please>]

Cesar Rabak wrote:
> Niklas Holsti escreveu:
> ...
>>  ...
>> So here is my try at an Ada version of the code and some of the 
>> context. ...
> 
> 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.

Well, I would like to hear your stylistic views, too... even if no 
objective right or wrong can be judged.

>> ...  It would be interesting to compile this code with AVR-Ada;
> 
> 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)."

Yes, so the exception-raising form of ADC.Thermometer.Temperature would 
have to be excluded. Luckily :-) there is the other form with a variant 
record type.

To diverge a bit, it would be lovely if some intrepid academic with 
access to hordes of eager students would give them a project to port the 
Open Ravenscar Kernel (ORK) to the AVR for use with AVR-Ada. That would 
give us tasking, at least.

> [snipped]
> 
>>       type Celsius_T is delta 0.1 digits 5 range -40.0 .. 120.0;
> 
> 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.

Gnat (3.15p on Debian, target native Intel x86) accepts a 'Size clause 
of 12 bits for this type. I don't see why a compiler targeted to a 
microcontroller should use a larger representation. I'm not expert in 
fixed-point arithmetic implementations but I think addition and 
subtraction can be done without using larger intermediate 
representations, and the example program has no multiplication or 
division operations with this type (it has Celsius_T * Natural, but that 
  does not need special scaling).

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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