Array bounds checks

[Cedric Berger]

"Boehm, Hans" wrote:
> 
> > Currently we can't implement that because our array header is attached
> > directly to the data.  We'd have to add an indirection to make
> > contiguous multidimensional arrays work.
> >
> I don't think I understand the problem.  You would allocate the same objects
> as now, except all in one contiguous chunk.  I.e. you'd get something like
> 
> Main array header (includes a "contiguous" tag)
> Main array (containing pointers to subarrays)
> 0th subarray header
> 0th subarray
> 1st subarray header
> ...
> 
> It should still be possible to locate the [i,j] element with a
> multiplication and a couple of additions.  There are some slightly
> unfortunate GC implications, but you could easily make this optional.  Even
> if you make the decision at run-time, the main cost is dead code.
> 

I'm wrong in saying that even if the multiarray has been initially
allocated rectangular, that fact can be changed later, i.e.:

double[][] array = new double[10][10];

later...

array[2] = new double[20];

Which poses some slight problem with this approach...

Cedric