|
|
Glas :Re: [glas] backend selection policies |
From: Karl Meerbergen (Karl.Meerbergen_at_[hidden])
Date: 2006-02-03 03:38:45
Toon Knapen wrote:
>Hi all,
>
>I just checked in support for backend-selection policies (tested on
>mult_scalar_assign functor). Such policies allow the user to say to
>dispatch a specific call to blas (and return an error if the call can
>not be handled by blas), or to try to dispatch to blas and otherwise
>dispatch to glas etc.
>
>For instance, take following code fragment:
><code>
>glas::dense_vector< std::complex<double> > v(10) ;
>std::complex< double > scalar(1,1) ;
>glas::mult_assign_scalar< glas::backend_blas_glas >( v, scalar ) ;
></code>
>
I would also allow adaptors (or policy selectors) so that we can use the
syntax
backend_blas_glas( v ) *= scalar ;
where
v *= scalar ;
uses the default backend.
The left hand side then decides that the expression on the right-hand
side is evaluated with this backend.
A similar mechanism can be used for assignment policies.
The advantage is that the choice of backend can be used with operators
as well.
Other syntaxes have been proposed: v[backed_blas_glas] *= scalar
but I am not very keen on using the operator[] for this purpose.
Karl
>
>In line 3, the 'mult_assign_scalar' function is called with the
>backend-selection-policy as a template argument (in this case
>'glas::backend_blas_glas'). This policy dictates that first the
>dispatching mechanism should first evaluate if the call can be
>dispatched to a blas equivalent (at compile-time using boost::mpl
>functionality etc). If no blas equivalent is available, the policy says
>to fallback to the generic glas implementation. Thus line 3 will
>actually call 'zscal' in this case.
>
>Suppose however that the vector 'v' is a vector of integers (instead of
>double-complex), no BLAS equivalent exists. In that case the
>'glas::backend_blas_glas' policy will detect that the call is not
>directly supported by blas and will then dispatch to the generic glas
>implementation.
>
>I guess support for such policies allow the requisted flexibility
>regarding the integration/selection of backends. If not, let me know.
>
>toon
>_______________________________________________
>glas mailing list
>glas_at_[hidden]
>http://lists.boost.org/mailman/listinfo.cgi/glas
>
>
>
-- ============================================== Look at our unique training program and Register on-line at http://www.fft.be/?id=35 ---------------------------------------------- Karl Meerbergen Free Field Technologies NEW ADDRESS FROM FEBRUARY 1st ONWARD: Axis Park Louvain-la-Neuve rue Emile Francqui, 1 B-1435 Mont-Saint Guibert - BELGIUM Company Phone: +32 10 45 12 26 Company Fax: +32 10 45 46 26 Mobile Phone: +32 474 26 66 59 Home Phone: +32 2 306 38 10 mailto:Karl.Meerbergen_at_[hidden] http://www.fft.be ============================================