Re: Efficiency of code generated by Ada compilers

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 6 Aug 2010 13:21:48 -0700 (PDT), Elias Salom�o Helou Neto wrote:

> I would like to know how does code generated by Ada compilers compare
> to those generated by C++.

The short answer is yes, of course.

The long answer is that such comparisons are quite difficult to perform
accurately.

> I use C++ for numerical software
> implementation, but I am trying to find alternatives.

Ada is especially good for this, because it has an elaborated system of
numeric types with specified accuracy and precision (and behavior), which
C++ lacks.

> One thing,
> however, I cannot trade for convenience is efficiency. Will Ada
> compiled code possibly be as efficient as that generated by C++
> compilers?

Certainly yes. Potentially Ada code can be more efficient, because in Ada
your program usually tells the compiler more than in C++. This information
can be used in optimization.

> Also, I do need to have something similar to C++ "templated
> metaprogramming" techniques.

Ada has generics which are roughly same as templates. Unlikely to C+
generics are contracted and not automatically instantiated.

> In particular, C++0x will introduce
> variadic templates, which will allow us to write templates that will
> generate efficient, type-safe, variable-argument functions. Is there
> anything like that in Ada?

No.
 
> If any of the above questions is to be negatively answered, I ask: why
> does Ada even exist?

Do you mean variadic templates here? Seriously?

> And further, is there any language which is
> _truly_ better (regarding code maintainability, readability and
> developing ease) than C++ and as overhead-free as it?

Maintainability, readability and developing ease are sufficiently dependent
on *not* using things like C++ templates. Even more variadic templates!

Note that for numeric applications templates do not help much. Consider the
following problem. Let you have to implement some mathematical function of
known algorithm and put it into a library. That latter is not possible with
templates anyway is beside the point. How do you do it to work for say
float, double etc? Metaprogramming you said. You could try implementing it
as a template<class number>, but the parameter here is not the actual type
you need to use in the computations in order to make the result accurate
within the precision of the type number. In C++ you cannot even learn the
precision of a template argument. In Ada at least you can (Ada Reference
Manual 3.5.8). But considering:

generic
   type Real is digits <>;  -- To work with any floating-point type
function Generic_Elliptic_Integral (X : Real; K : Real) return Real;

The following implementation is illegal:

function Generic_Elliptic_Integral (X : Real; K : Real) return Real is
   type Internal is digits Real'Digits * 2;  -- You cannot do that!
begin
   ...

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