From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,d679dd7e9c16805a
X-Google-Attributes: gid103376,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news1.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!nx02.iad.newshosting.com!newshosting.com!newspeer.monmouth.com!newsswitch.lcs.mit.edu!nntp.TheWorld.com!not-for-mail
From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Selective suppression of warnings --- gnat on GNU/Linux
Date: Wed, 31 Dec 2008 17:38:35 -0500
Organization: The World Public Access UNIX, Brookline, MA
Message-ID: <wcc3ag4ezro.fsf@shell01.TheWorld.com>
References: 
 <7a6baa71-80e8-4f3a-80b6-34935bda2fc0@r10g2000prf.googlegroups.com>
 <wccr63p1cke.fsf@shell01.TheWorld.com> <42ffjg.s9b.ln@hunter.axlog.fr>
 <C5816DB9.1065AB%yaldnif.w@blueyonder.co.uk>
 <wcchc4kyvkh.fsf@shell01.TheWorld.com> <oyQ6l.504823$yE1.127677@attbi_s21>
NNTP-Posting-Host: shell01.theworld.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: pcls4.std.com 1230763115 18115 192.74.137.71 (31 Dec 2008 22:38:35
 GMT)
X-Complaints-To: abuse@TheWorld.com
NNTP-Posting-Date: Wed, 31 Dec 2008 22:38:35 +0000 (UTC)
User-Agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.3 (irix)
Cancel-Lock: sha1:2BUlN1Rd+JRq6yYrmkv4uKEQWrE=
Xref: g2news2.google.com comp.lang.ada:4132
Date: 2008-12-31T17:38:35-05:00
List-Id: <comp.lang.ada>

"Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org> writes:

> Robert A Duff wrote:
>> More generally, it would also be nice to have a way to say, "Give me a
>> number that would be appropriate as the upper bound of an array whose
>> component type is T."  The number would be guaranteed to be big enough
>> that you would get Storage_Error if you ever create an array that big.
>
> Isn't that approximated by System.Max_Int and System.Max_Binary_Modulus?

Well, the RM doesn't say that, and it's not true on at least some
implementations.  For example, GNAT on a 32-bit machine has
System.Max_Int = 2**63-1.  But if I want a possibly large
array of Integers, I want something like:

    type Index is range 1..2**31-1;
    type A is array (Index range <>) of Integer;

Or I might want 2**32-1, but 2**63-1 is way too big for a 32-bit
machine, and would be unnecessarily inefficient.

> On many modern processors and OSes, though, one could possibly have a
> packed array of Boolean with those bounds that would fit in the
> available memory. But since you can't create an integer type with more
> values, the desired effect would be impossible to achieve.

Good point.

On a 64-bit machine, you have enough virtual memory to create a packed
array of 2**63-1 Booleans (2**60 bytes), but you don't have enough
physical memory, or even paging file, to store it.

- Bob