> these arrays grow themselves exponentially
Are you sure about this? Where did you get this information?
As far as I can tell by looking at mscorlib.dll using dis-compiler,
ArrayList.Add() uses:
if (this._size == (int) this._items.Length)
this.EnsureCapacity(this._size + 1);
-----Original Message-----
From: Moderated discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED]] On Behalf Of Ian Griffiths
Sent: Sunday, July 07, 2002 3:22 AM
To: [EMAIL PROTECTED]
Subject: Re: [ADVANCED-DOTNET] Specifying an initial capacity hurts
performance [was Benchmark]
"David Ferguson" <[EMAIL PROTECTED]> wrote:
>
> Certainly in this test (large array, constant value) it
> does appear to be slower (not significantly, but a little).
>
> >By value, dynamically reallocated | >By value, preallocated
> | (with pause between test)
> >----Test 0 | >----Test 0
> >Elapsed 640 ms | >Elapsed 661 ms
> >----Test 1 | >----Test 1
> >Elapsed 590 ms | >Elapsed 651 ms
> >----Test 2 | >----Test 2
> >Elapsed 691 ms | >Elapsed 651 ms
> >----Test 3 | >----Test 3
> >Elapsed 621 ms | >Elapsed 651 ms
> >----Test 4 | >----Test 4
> >Elapsed 601 ms | >Elapsed 651 ms
> ---------------------- ------------------------------
> average 629 average 653
But the variance is pretty huge on your first column there. I think the
different of 24ms is swamped by the uncertainty in the measurements.
So with your data I came to the same conclusion as I did with my data:
it's difficult to tell which, if either, is faster, without more
extensive measurement and careful analysis.
This is what you would expect - the difference in allocation count for
preallocation will only amount to a fairly small number (these arrays
grow themselves exponentially, so the number of allocations is small).
So you'd expect it to be too small to measure easily.
--
Ian Griffiths
DevelopMentor
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