[fpc-pascal] about dynamic array

José Mejuto joshyfun at gmail.com
Sat May 8 20:44:20 CEST 2010

Hello FPC-Pascal,

Saturday, May 8, 2010, 4:42:46 PM, you wrote:

VH> So, apart from a possibly more optimized implementation (like
VH> not changing the allocated memory size on each single
VH> insertion/deletion) how do you come up with the idea that adding
VH> another layer would make it faster?

Because it is not "another layer", is a different implementation. You
say that my implement was not fair play as I use "SetLength" inside
the loop, but the user request fast insertion/deletion so he do not
known in advance the amount of items in the array. The code to insert
something in a Dyn array is more complex than a remove in TList.

Using dyn arrays and some helper functions to insert/delete elements
would be faster and using a helper variable to get the amount of
cached entries (not filled) and real entries will end in faster code
for sure, but more complex from the end user point of view. TList
version imposes more memory fragmentation (each element is in its own
block) which could be convenient or not based in the amount of memory
available and the current fragmentation (big blocks are not always the
better solution).

I take the time to peform the test suggested in previous mail,
allowing the dyn array to known the amount of elements available in
advance, and here are the results:

Elements  Record of bytes  Dyn array  TList
--------  ---------------  ---------  --------
1000000      64            187 ms     1328 ms
 100000    4096            1032 ms    1046 ms
 100000    4095            1469 ms    1031 ms
 100000   16384            Crash      5954 ms
  10000   65536            1656 ms    2188 ms
  10000   65537            2312 ms    2219 ms

The "crash" was due there was not available 1.5 Gby available in one

I can post the code if you like.

Best regards,

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