Re: Compile time executed functions

[Mats Karlssohn <mats@mida.se>]

Ken Garlington wrote:
%<
> : Say I want to create a table of data. The data is constant and must not
> : change during the programs lifetime. Further more, the data is quite
> : time consuming to calculate.
> :
> : In C++ (bad word again :) I can (with some effort) write a template that
> : does all the calculations in the compiler at compile time.
> 
> Could you post an example of such a template, and what in the C++ standard
> you rely upon to guarantee compile-time calculations? Also, does
> "compile-time" include "link-time", or are you not allowed to have anything
> in the table that uses addresses?

Well.. no. I must admit (quite embarresed) that I can't, I spent a few
hours during the weekend trying to put together an example, but I
couldn't
get it to work. However (and more importantly) I've seen such a thing
done, I just havn't acces to that sourcecode anymore, so I really can't
examine it. Bugger, it might be that I'm plain wrong and have fallen for
some 'good talk for the project management' (I'm NOT the manager,
but...)



> It's the part about "pasting the output" that seems odd. Why not have it
> generate a stand-alone Ada *package* (e.g, BlahBlah)? We do this now in a
> number of cases. In fact, you can have an automated build script that
> generates the code, updates the CM system with it, then does the things you
> usually expect in such a script (extract source from CM system, compile,
> link...)

Yes, I could, but:
1. I'm too lazy to do it.
2. There's quite a lot of other code/data in the package.

But this actually gives me an idea, my data table could be separate,
right ? That would render the output from the tool so small that I
actually could generate the whole source file, so that no handediting
is needed. I'll need to investigate this.

> : Am I plain stupid since I worry about when what's included in my
> : output and when time is consumed ?
> 
> Not at all. However, the source generation option can be just as reliable
> (more so, since it's less dependent on compiler-specific optimizations) that
> whjat you are wanting, IMHO. Even better, you can readily reuse the concept
> if you move between languages (just have the source generation tool use a
> template file to control the form of the output).

OK

I thought that i had decided to let the tool produce an (ELF) object
file
and just pragma Import(..) a symbol from that. Now I'll investigate and
reconsider.

-- 
Mats Karlssohn, developer                         mailto:mats@mida.se  
Mida Systemutveckling AB                          http://www.mida.se
Box 64, S-732 22 ARBOGA, SWEDEN
Phone: +46-(0)589-89808   Fax: +46-(0)589-89809