Re: [PATCH] Replace loop by memset in sal/typesconfig/typesconfig.c

On 12/24/2012 06:44 PM, Julien Nabet wrote:
> On 24/12/2012 18:29, Norbert Thiebaud wrote:
> > On Mon, Dec 24, 2012 at 8:45 AM, julien2412<serval2412@yahoo.fr>  wrote:
> > > By taking a look at the file  sal/typesconfig/typesconfig.c,
> > > GetAlignment
> > > function, I wonder if we could replace the for loop by a memset to
> > > optimize
> > > a bit.
> > > So here's a straightforward patch:
> > > diff --git a/sal/typesconfig/typesconfig.c
> > > b/sal/typesconfig/typesconfig.c
> > > index 473f07a..ef52c5f 100644
> > > --- a/sal/typesconfig/typesconfig.c
> > > +++ b/sal/typesconfig/typesconfig.c
> > > @@ -262,11 +262,9 @@ int GetAlignment( Type eT )
> > >   {
> > >     char  a[ 16*8 ];
> > >     long  p = (long)(void*)a;
> > > -  int   i;
> > >
> > >     /* clear a[...] to set legal value for double access */
> > > -  for ( i = 0; i<  16*8; i++ )
> > > -    a[i] = 0;
> > > +  memset(a, 0, sizeof(a));
> > >
> > >     p = ( p + 0xF )&  ~0xF;
> > >     for ( i = 1; i<  16; i++ )
> > >
> > > Would it be ok?
> > well you can't remove
> >   int i;
> >
> > since it is still used in the second for loop.
> >
> > and I doubt that that code is run very often... namely 4 times per
> > execution of the typesconfig executable... which in turn run dozens of
> > fprintf...
> > I'd say that this micro-optimization would be completely
> > un-measurable, and may or may not be an optimization at all depending
> > on how the memset is treated.
> > but sure, it is 'ok', as in it won't hurt anything.

The benefit of memset over an explicit loop here would be shorter, more 
obvious (IMO) code, so I'd suggest you do the change after all.

Stephan

> ok let's forget it, I suppose that the one who made this loop has
> certainly good reasons for this + you must be right, micro-optimization