Re: Fortran vs C++ vs. etc (has little to do with realtime anymore)

[Oleg Krivosheev <kriol@fnal.gov>]

Hi,

Constantine Antonovich: <const@orbotech.co.il> writes:

> 
> Oleg Krivosheev wrote:
> > 
> > [skipped]
> > 
> > sorry, i have only min ;)
> > 
> > well, try example below for min with
> > arbitrary larger number of arguments. Hope it can help
> > 
> > #include <assert.h>
> > #include <stdio.h>
> > #include <stdarg.h>
> > 
> > double
> > dmin( int nofargs, ... ) {
> > 
> >   double res = 1.0e+38, arg;
> >   int j;
> >   va_list ap;
> > 
> >   assert( nofargs > 1 );
> > 
> >   va_start(ap, nofargs );
> > 
> >   for( j = 0; j < nofargs; ++j ) {
> >     arg=va_arg( ap, double );
> >     if ( arg < res ) {
> >       res = arg;
> >     }
> >   }
> >   va_end(ap);
> >   return res;
> > }
> > 
> > int
> > main( void ) {
> > 
> >   printf( "%e\n", dmin( 2, 1.0, 2.0 ) );
> > 
> >   printf( "%e\n", dmin( 3, 0.0, 1.0, 2.0 ) );
> > 
> >   printf( "%e\n", dmin( 5, 0.0, 1.0, 2.0, 7.0, -0.2 ) );
> > 
> >   return 0;
> > }
> > 
> > [skipped]
> > 
>     OK, just to be pedantic, the previous  example shows very fine
> the  difference  between  fortran and  C    in computations. Since

gu ?

> min/max are  standard fortran functions, it  can be  supposed they
> are maximally   optimized  with no  regards  to   number  of their
> arguments (just because the compiler takes care of them).

well, FYI, being standard means only that - being standard.
Compiler is free to optimize or to insert 5min  loop
into min/max function.

>     In the  contrary,   in the example,  we  have overhead of  the
> arguments  number  evaluation 

sure...

if you know how do not evaluate number of arguments
for functions (not min/max in particular) with arbitrary
number of arguments, please share your knowledge with us.

> and overhead of  implementation (not
> necessarily    this   one,  generally   almost    any  non-trivial
> non-built-in operation has  some overhead -   there has been  some
> reason   to  add  into  C  libraries  memcpy,   memcmp  and so  on
> functions).

what do you mean "overhead"? Can you clarify ?

>     Using  C++ and not C, most  probably, I would try to implement
> the min function in the following way:
> 
> inline double min(double v1, double v2) {
>   return v1<v2 ? v1 : v2;
> }
> inline double min(double v1, double v2, double v3) {
>   double v=min(v1,v2); return v<v3 ? v : v3;
> }
> inline double min(double v1, double v2, double v3, double v4) {
>   double v=min(v1,v2,v3); return v<v4 ? v : v4;
> }
> inline double min(double v1, double v2, double v3, double v4, double v5)
> {
>   double v=min(v1,v2,v3,v4); return v<v5 ? v : v5;
> }

please, don't change the nature of the problem - Rick
was asking about min/max function with ARBITRARY
number of arguments.

>     Such  a way  doesn't seem elegant enough and it only  emulates
> arbitrary number

nope. it's not. If the problem is to provide function
which can handle arbitrary number of arguments,
it cannot be solved by providing function(s) which
can handle limited number of arguments. Try to reread
logic textbook next time.

>   started  on SunOS 5.5.1 SUNW,Ultra-2 produces
>     dmin: 3.04 seconds
>     overloaded min: 1.11 seconds
>   started on SunOS 5.5.1 SUNW,SPARCstation-4 produces:
>     dmin: 9.32 seconds
>     overloaded min: 4.89 seconds
> and compiled  with -O option with HP  C++  A.03.72; and started on
> HP-UX A.09.05 9000/715 produces:
>     dmin: 4.63 seconds
>     overloaded min: 1.58 seconds

well, you compare apples and oranges.

You provided solution for related but
another problem than Rick was asking for.

still, you know better way to handle
functions with arbitrary number of
arguments (using C++, templates, exceptions
whatever), please, share it with us.

OK