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Re: Memory, objects, and TCollections

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From	Marco van de Voort <marcov@toad.stack.nl>
Newsgroups	comp.lang.pascal.borland
Subject	Re: Memory, objects, and TCollections
Date	Fri, 27 Jul 2012 10:46:38 +0000 (UTC)
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On 2012-07-26, Jim Leonard <MobyGamer@gmail.com> wrote:
> This project must run on 808x systems, so no.

Dataintensive apps with those limitations, that is setting yourself up for
disaster, but let's take it as a given.

One of the problems then is that the hardwiring of ems/xms support, while
8086 compatible also adds limitations.  You can't rely on it too much and
essentially use mainmem as a paging buffer, because what if it is missing or
very limited in size like on XTs and older 286s?

>> Inserting an item in larger collections becomes very slow because
>> it has to move (on average) n/2 items.
>
> Right, but it's only moving a 4-byte pointer so it's not that bad.  I have the RTL and I peeked at the implementation -- it's just an array of pointers.

That should have been on /ordered/ collections.

If you load unsorted data and insert them into a TP TSorted* or Delphi TStringlist,
since the average item will insert in the middle of the list, there are
sizeof(pointer)* (N/2) bytes to move to make room for them.

So for N items that becomes a sizeof(pointer)*N^2/2 iow O(N^2) operation.

But as said typically you only start to notice it at hundreds of thousands
of items, and afaik standard TP datatypes are limited to 64k, so 16384 items
max.

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Thread

Memory, objects, and TCollections Jim Leonard <mobygamer@gmail.com> - 2012-07-22 11:02 -0700
  Re: Memory, objects, and TCollections Marco van de Voort <marcov@toad.stack.nl> - 2012-07-22 21:07 +0000
    Re: Memory, objects, and TCollections Robert AH Prins <spamtrap@prino.org> - 2012-07-23 02:31 +0000
      Re: Memory, objects, and TCollections Jim Leonard <mobygamer@gmail.com> - 2012-07-23 11:33 -0700
        Re: Memory, objects, and TCollections Marco van de Voort <marcov@toad.stack.nl> - 2012-07-24 16:20 +0000
          Re: Memory, objects, and TCollections Jim Leonard <MobyGamer@gmail.com> - 2012-07-26 14:19 -0700
            Re: Memory, objects, and TCollections Marco van de Voort <marcov@toad.stack.nl> - 2012-07-27 10:46 +0000
    Re: Memory, objects, and TCollections Jim Leonard <mobygamer@gmail.com> - 2012-07-23 11:42 -0700
      Re: Memory, objects, and TCollections Marco van de Voort <marcov@toad.stack.nl> - 2012-07-25 12:10 +0000
        Re: Memory, objects, and TCollections Jim Leonard <MobyGamer@gmail.com> - 2012-07-26 14:21 -0700
          Re: Memory, objects, and TCollections Marco van de Voort <marcov@toad.stack.nl> - 2012-07-27 11:13 +0000

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