Im a relatively new coder and am still learning the best way to do thigs

- and I have always been told the best way to learn is by writing

testing code and measuring, Could anyone shed some light on why my

'MyArray[,,]' test is so much faster? Id really like to know!

What is the best method for creating and accessing 2D, 3D and nD arrays?

Cheers Guys

Jon Rea

Application Output

WindowsXP:

Sum: 251437500.000000

Sum: 251437500.000000

Array3D test Took 30 seconds

Sum: 251437500.000000

Sum: 251437500.000000

MyArray[] test Took 30 seconds

Sum: 251437500.000000

Sum: 251437500.000000

MyArray[] (V2) test Took 29 seconds

Sum: 251437500.000000

Sum: 251437500.000000

MyArray[,,] test Took 11 seconds

Linux (RH9):

Sum: 251437500.000000

Sum: 251437500.000000

Array3D test Took 20 seconds

Sum: 251437500.000000

Sum: 251437500.000000

MyArray[] test Took 20 seconds

Sum: 251437500.000000

Sum: 251437500.000000

MyArray[] (V2) test Took 22 seconds

Sum: 251437500.000000

Sum: 251437500.000000

MyArray[,,] test Took 6 seconds

Application Code

#include <iostream>

#include <stdio.h>

#include <tchar.h>

#include <time.h>

#include "tntjama/tnt_array3d.h"

using namespace TNT;

int _tmain(int argc, _TCHAR* argv[])

{

int count1 = 15;

int count2 = 100;

int M = 150;

int N = 150;

int P = 150;

time_t starttime = time( NULL );

for( int r = 0; r < count1; r++ )

{

Array3D< double A(M,N,P);

for (int i=0; i < M; i++)

for (int j=0; j < N; j++)

for (int k=0; k < P; k++)

A[i][j][k] = (double)k; /* initalize

array values */

for( int q = 0; q < count2; q++ )

{

double sum = 0.0;

for (int i=0; i < M; i++)

for (int j=0; j < N; j++)

for (int k=0; k < P; k++)

sum += A[i][j][k]; /* calc sum */

if( r == 0 && (q == 0 || q == 15) ) printf("Sum: %lf\n",sum);

}

}

printf("Array3D test Took %d seconds\n",(int)(time(NULL) - starttime));

starttime = time( NULL );

int T = M*M;

for( int r = 0; r < count1; r++ )

{

double *A = new double[M*N*P];

for (int i=0; i < M; i++)

for (int j=0; j < N; j++)

for (int k=0; k < P; k++)

A[(T*i)+(N*j)+k] = (double)k; /*

initalize array values */

for( int q = 0; q < count2; q++ )

{

double sum = 0.0;

for (int i=0; i < M; i++)

for (int j=0; j < N; j++)

for (int k=0; k < P; k++)

sum += A[(T*i)+(N*j)+k]; /* calc sum */

if( r == 0 && (q == 0 || q == 15) ) printf("Sum: %lf\n",sum);

}

delete[] A;

}

printf("MyArray[] test Took %d seconds\n",(int)(time(NULL) -

starttime));

starttime = time( NULL );

T = M*M;

int indexRoot1, indexRoot2;

for( int r = 0; r < count1; r++ )

{

double *A = new double[M*N*P];

for (int i=0; i < M; i++)

{

indexRoot1 = (T*i);

for (int j=0; j < N; j++)

{

indexRoot2 = indexRoot1 + (N*j);

for (int k=0; k < P; k++)

{

A[indexRoot2+k] = (double)k; /*

initalize array values */

}

}

}

for( int q = 0; q < count2; q++ )

{

double sum = 0.0;

int indexRoot1, indexRoot2;

for (int i=0; i < M; i++)

{

indexRoot1 = (T*i);

for (int j=0; j < N; j++)

{

indexRoot2 = indexRoot1 + (N*j);

for (int k=0; k < P; k++)

{

sum += A[indexRoot2+k]; /* calc sum */

}

}

}

if( r == 0 && (q == 0 || q == 15) ) printf("Sum: %lf\n",sum);

}

delete[] A;

}

printf("MyArray[] (V2) test Took %d seconds\n",(int)(time(NULL) -

starttime));

starttime = time( NULL );

for( int r = 0; r < count1; r++ )

{

double *A = new double[M,N,P];

for (int i=0; i < M; i++)

for (int j=0; j < N; j++)

for (int k=0; k < P; k++)

A[i,j,k] = (double)k; /* initalize

array values */

for( int q = 0; q < count2; q++ )

{

double sum = 0.0;

for (int i=0; i < M; i++)

for (int j=0; j < N; j++)

for (int k=0; k < P; k++)

sum += A[i,j,k]; /* calc sum */

if( r == 0 && (q == 0 || q == 15) ) printf("Sum: %lf\n",sum);

}

delete[] A;

}

printf("MyArray[,,] test Took %d seconds\n",(int)(time(NULL) -

starttime));

return 0;

}