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From: Jacob Sparre Andersen <sparre@nbi.dk>
Newsgroups: comp.lang.ada
Subject: Re: Copying string slices before calling subroutines?
Date: Fri, 04 May 2007 11:44:14 +0200
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Date: 2007-05-04T11:44:14+02:00
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Jacob Sparre Andersen wrote:
> Dmitry A. Kazakov wrote:
>> On Fri, 04 May 2007 08:53:59 +0200, Jacob Sparre Andersen wrote:

>>>      for Lines in 1 .. 10 loop
>>>         Last := Index (Source  => Text (Text'First .. Last - 1),
>>
>> Did you check if GNAT did not copy the string slice before calling to
>> Index?
>
> No.  Do you have any suggestion for a way to check it.  The
> reference manual (section 6.2) seems to indicate that it is up to
> the compiler to decide.

I have found a strong indication that GNAT copies the whole string
slice onto the stack before calling Index:

It is limited how large files I can run my Tail program on, before I
get a segmentation fault.  The limit is roughly the allowed stack size
on the system (and changes as I change the allowed stack size).

This version appears to be as fast as the GNU Tail program.  The only
thing which worries me a bit is that I see roughly twice as many
"minor pagefaults" with my own version as with the GNU version.

Greetings,

Jacob

PS: I don't feel like cheating and looking at the GNU source code yet.
-- 
"Then, after a second or so, nothing continued to happen."