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From: Vadim Godunko <vgodunko@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT's stack checking in Ubuntu 9.04 (and Shootout regex-dna)
Date: Tue, 4 Aug 2009 05:30:07 -0700 (PDT)
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Date: 2009-08-04T05:30:07-07:00
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On Aug 4, 2:44=A0pm, Georg Bauhaus <rm.dash-bauh...@futureapps.de>
wrote:
> It hits the limit exaclty when the array of 625_000
> default initialized Vstrings is allocated on the stack.
> No operations performed at that point.
>
> > Unbounded_String uses constant size of stack for object itself and
> > uses dynamic size on heap for actual value.
>
> Yes. How much does a default initialized Unbounded_String
> use when it is an array component? (I'll debug this when
> there is more time; just in case you happen to know,
> would be most helpful.)
>
Its very easy to discover:

with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
package Tst is
   type T is array (Positive range <>) of Unbounded_String;
   X : T (1 .. 625_000);
end Tst;

> gcc -c -gnatR3 tst.ads

Representation information for unit Tst (spec)
----------------------------------------------

for T'Alignment use 16;
for T'Component_Size use 512;

for X'Size use 320000000;
for X'Alignment use 16;

So, on my platform (OpenSUSE Linux/x86_64) array of Unbounded_String
with 625_000 components occupy approximately 40Mb.