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Re: [Help-gsl] Questions about the code of some functions in cblas imple

From: Brian Gough
Subject: Re: [Help-gsl] Questions about the code of some functions in cblas implementation
Date: Thu, 18 Jun 2009 20:49:50 +0100
User-agent: Wanderlust/2.14.0 (Africa) Emacs/22.2 Mule/5.0 (SAKAKI)

At Wed, 17 Jun 2009 13:31:10 +0200,
José Luis García Pallero wrote:
> Surfing the source code of some functions of cblas implementation I found:
> 1- In source_scal_r.h, _c_s.h and _c.h I think that the sentence ix =
> OFFSET(N, incX); is not needed because the functions only works when incX is
> greater than 0 and, in this case, OFFSET(N, incX) allways returns 0.

You're right, I will remove that unnecessary line. Thanks.

> 2- I can see that, as in the original BLAS, *axpy functions has loop
> unrolling by hand. Is this nessesary today with the optimizations of the
> copiler? I can see in other functions of the gsl-cblas that unrolling is not
> used (though in the original fortran BLAS is still used).

As you say, it is probably not needed with a recent compiler. I don't
know whether it does any harm to leave it though (has anyone tried a
comparison?).  I am tempted to #ifdef it out and replace it with a
plain loop.

Brian Gough
(GSL Maintainer)

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