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Re: Array operations in C

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On Tue, Apr 07, 2015 at 04:24:34PM +0100, Bartc wrote:
> On 07/04/2015 15:10, Bartc wrote:
> >On 07/04/2015 14:06, beliavsky@aol.com wrote:
> 
> >>Intel C and C++ now support array operations such as the following:
> >>
> >>r[0:n] = 0;
> >>for( int j = 0; j < ncols; ++j )
> >>   r[0:n] += a[rowndx[0:n]+j] * v[colndx[rowndx[0:n]+j]];
> >>
> >>What is the chance that such operations become part of standard C and
> >>are implemented in gcc?
> >
> >Small.
> >
> >But, assuming that r[0:n] means n elements of r starting from r[0],
> >these map very easily to a normal loop:
> >
> >  r[0:n] = 0;
> >
> >becomes:
> >
> >  for (k=0; k<n; ++k)
> >     r[k] = 0;
> 
> A general slice such as r[a:len] is slightly trickier:
> 
>     for (k=a; k<(a+len); ++k)
>        r[k] = 0;
> 
> So it starts to have more value (although an apt macro can take care of 
> that too). But perhaps somewhat more useful is being able to operate on 
> the entire array:
> 
>       r[:] = 0; // or some such syntax
> 
> this is harder to implement conventionally because there needs to be a 
> way of picking up the length, and for dynamic arrays this is not stored 
> anywhere it can be grabbed automatically.
> 
> Maybe Intel C (and was that Intel C++ too?) have sorted that, however 
> then it becomes a far more fundamental change to the language than more 
> concise syntax. In other words, it's never going to happen! (Maybe in 
> C++, but there apparently anything goes.)

Perhaps.  But it seems obvious to me that parallel programming will
become the norm rather than the exception and it is reasonable to
suggest that languages will naturally adjust to that paradigm as much
as they are able.  What that portends for C is another matter.

OpenMP and such are only half of the (potential) solution.  Exploiting
parallelism among cooperating nodes is the other half of the equation
and that remains difficult.  Perhaps a multi-node shared/virtual
memory system will emerge that is analogous to today's hardware
assisted VM systems, including a largely transparent message-passing
architecture.  It would be very convenient to address local and
foreign threads transparently, but the basic problem of latency would
seem to make that fundamentally problematic.




Regards,

Steve Thompson

-- 
"If I had a nickel for every time some idiot called me about a
computer problem that turned out to be user error, I would be able to
retire and spend the rest of my days cultivating clues in my backyard
hillside garden."  -- MysteryDog in 24hoursupport.helpdesk.

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Array operations in C beliavsky@aol.com - 2015-04-07 06:06 -0700
  Re: Array operations in C Bartc <bc@freeuk.com> - 2015-04-07 15:10 +0100
    Re: Array operations in C Bartc <bc@freeuk.com> - 2015-04-07 16:24 +0100
      Re: Array operations in C Steve Thompson <stevet810@gmail.com> - 2015-04-09 00:35 +0000
    Re: Array operations in C fir <profesor.fir@gmail.com> - 2015-04-08 07:48 -0700
  Re: Array operations in C Tim Prince <tprince@computer.org> - 2015-04-07 10:30 -0400
  Array operations in C asetofsymbols@gmail.com - 2015-04-07 08:00 -0700
    Array operations in C asetofsymbols@gmail.com - 2015-04-07 08:09 -0700
      Array operations in C asetofsymbols@gmail.com - 2015-04-07 08:36 -0700
        Array operations in C asetofsymbols@gmail.com - 2015-04-07 08:58 -0700
        Array operations in C asetofsymbols@gmail.com - 2015-04-08 00:16 -0700
          Array operations in C asetofsymbols@gmail.com - 2015-04-08 01:30 -0700
          Re: Array operations in C Tim Prince <tprince@computer.org> - 2015-04-08 08:59 -0400

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