Re: Efficiency of code generated by Ada compilers

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

On Mon, 16 Aug 2010 06:29:42 -0700 (PDT), Elias Salom�o Helou Neto wrote:

> Well, in such a case C could do the job, right?

Everything is Turing-Complete...

> Encapsulating the low-
> level array implementation within well designed classes, possibly
> templated ones, would be a much better idea, would not?
> 
> What I meant from the beginning was to possibly write code such as
> (sorry for the C++ syntax):
> 
> Matrix< 3, double > volumeImage( 100, 100, 100 );
> Matrix< 2, char > asciiArt( 50, 75 );
> 
> asciiArt( 10, 10 ) = a;
> volumeImage( 1, 2, 3 ) = 5.7;

Well, maybe, but it is already done in Ada. Furthermore, the compiler
"knows" about arrays and can apply array-specific optimizations or take
advantage of array-specific processor instructions. Not that optimization
is my concern, but it seemingly is yours.

> Where those two or three dimensional members/constructors were
> automatically generated by the compiler by using "template
> metaprogramming". It will be possible with C++0x. It is already
> possible by using the experimental implementation of the new standard
> in GCC.

I don't see any gain, because this is trivial compared to the real
challenges of modeling linear algebraic types. Consider description of the
types on which the matrix multiplication is defined. E.g.: NxMxK * KxM = N.
Here NxM denotes matrix with dimensions N and M. Is it one type or many
types or many subtypes? Templates give no choice but many different
unrelated types, when dimensionality is a parameter. Not my choice. Now you
have a combinatorial explosion of overloaded variants. Generate them, all
possible multiplication operation profiles for 4D, 3D, 2D, 1D matrices.
Make the constraint on matrix size in given dimension statically enforced
with an appropriate (understandable!) error messages when sizes are
statically known. Allow unconstrained matrices as well. Generate aggregates
for each matrix type. Provide matrix slicing operations for all types of
matrices (e.g. column from matrix, row from matrix, submatrix from matrix
etc). Have fun!

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