Re: Memory limits in Ada where Fortran has none

["Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk>]

Hi!

This GNAT problem is coming up more frequently now with
more people wanting to use their 32-bit systems to the full :(

I regularly declare and use arrays in Ada which are 1.9GB, and
map directly to files (via POSIX mmap).  This is amazingly
fast for access to databases I need because I can directly
access all the elements in memory.

Unfortunately, my data sets ideally would be around 4-5GB, but
my Linux box wont mmap more than 2GB :(

The main caveats (IIRC) are:

Don't use 'Size type attributes on large records/arrays
Only use access values to the data
accessing record elements whose offset is > 256MB may be a problem(?) 

It's a big nuisance, because you can end up with programs which
compile OK, but fail at run-time.

I'm hoping someone will build an Athlon64 implementation of GNAT which
can make use of 64-bit access values.  I'm sure it will happen one day,
because 64-bit PCs will soon be ubiquitous, and the 256MB will become
a total embarrassment to the GNAT/Ada community.

Adrian
-- 
Dr. Adrian Wrigley, Cambridge, UK.