Boost::multi_array performance question

Question

I am trying to compare the performance of boost::multi_array to native dynamically allocated arrays, with the following test program:

#include 

        

Answer 1

On my machine using

g++ -O3 -march=native -mtune=native --fast-math -DNDEBUG test.cpp -o test && ./test

I get

[Boost] Elapsed time:  0.020 seconds
[Native]Elapsed time:  0.020 seconds

However changing const int ITERATIONS to 5000 I get

[Boost] Elapsed time:  0.240 seconds
[Native]Elapsed time:  0.180 seconds

then with ITERATIONS back to 500 but X_SIZE and Y_SIZE set to 400 I get a much more significant difference

[Boost] Elapsed time:  0.460 seconds
[Native]Elapsed time:  0.070 seconds

finally inverting the inner loop for the [Boost] case so it looks like

    for (int x = 0; x < X_SIZE; ++x)
    {
        for (int y = 0; y < Y_SIZE; ++y)
        {

and keeping ITERATIONS, X_SIZE and Y_SIZE to 500, 400 and 400 I get

[Boost] Elapsed time:  0.060 seconds
[Native]Elapsed time:  0.080 seconds

If I invert the inner loop also for the [Native] case (so it is in the wrong order for that case), I get, unsurprisingly,

[Boost] Elapsed time:  0.070 seconds
[Native]Elapsed time:  0.450 seconds

I am using gcc (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5 on Ubuntu 10.10

So in conclusion:

• With proper optimization boost::multi_array does its job as expected
• The order on which you access your data does matter