Re: optimization

Hector Santos <>
Tue, 16 Mar 2010 16:41:24 -0400
Bill Brehm wrote:

"Your choice of CArray is probably a Bad Idea."

It IS turning out to be a bad idea. This was one of the things I said I
would get around to asking. If I give a growby of 10000, the program runs at
a reasonable speed. When I set it much higher, like 100,000,000, thinking
that i'll have fewer reallocations, it runs really slowly. I would have
expected the opposite until 1e8 primes were calculated, then a large delay
during reallocation. But it's slow from the start. I did some
PerformanceQueries and found that adding something to the CArray (when it
grew by 10000) was ten times slow than doing a division as part of the prime
check. I don't know if it's a paging issue or some inefficiency in CArray
itself. I guess it's much worse with a large growby but i don't know why and
i didn't measure to check.

Bill, your solution is a memory map. Find yourself a good "CFileMap"
class that allows you to an element type to it and handles it as a
array. We have our own that allows us to do this:

    struct TArrayItems {
      int x;
      int y;

    CFileMap<TArrayItems> myArray;

    myArray.Open("some file name even temp");

    myArray[6].x = 1;
    myArray[6].y = 2;




Such a good class will use the CArray or any other collection class as
a base class for file mapping.


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