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From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.misc
Subject: Re: Answers, Chapter 2: to point or not to point
Message-ID: <6243:Nov720:29:4090@kramden.acf.nyu.edu>
Date: 7 Nov 90 20:29:40 GMT
References: <7006:Nov620:42:3990@kramden.acf.nyu.edu> <5088@lanl.gov>
Organization: IR
Lines: 27

In article <5088@lanl.gov> jlg@lanl.gov (Jim Giles) writes:
> From article <7006:Nov620:42:3990@kramden.acf.nyu.edu>, by brnstnd@kramden.acf.nyu.edu (Dan Bernstein):
> > In article <5073@lanl.gov> jlg@lanl.gov (Jim Giles) writes:
> >> |>       x(1,:) = x(2,:)
  [ I claim that this is an argument for array slices and copies, ]
  [ and has no bearing upon the pointer issue ]
> That's not the point.  The code (in existing languages) would
> have to be written as:

You are now *changing* what you said. I agree that your new version is
relevant to this thread. I emphasize that your original x(1,:) = x(2,:)
example was not.

>    Modula 2                     C
>       for i := 1 to N do           p = &x[1][0]; q = p+N;
> 	 x[1,i] := x[2,i]          for (i=0; i<N; i++)
>       end;                            *p++ = *q++;
> (Modula 2 this time - I did Fortran last time.) The pointer/C version is
> still be harder for the compiler to optimize.

I take back what I said about this being relevant to the thread: your C
code is incorrect.

I believe that if you stated it correctly, the Convex compiler would be
able to optimize it (specifically, vectorize it) the way you want.

---Dan