Benchmark

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/times.h>
#include <unistd.h>

//-- timer for benchmarks ------------------------------------------------------

double
walltime()
{
    struct tms    ts;
    static double ClockTick=0.0;

    if (ClockTick==0.0) {
        ClockTick = 1.0 / ((double) sysconf(_SC_CLK_TCK));
    }
    return ((double) times(&ts)) * ClockTick;
}

//------------------------------------------------------------------------------

void
initMatrix(size_t m, size_t n,
     double *A,
     ptrdiff_t incRow, ptrdiff_t incCol)
{
    for (size_t i=0; i<m; ++i) {
        for (size_t j=0; j<n; ++j) {
            A[i*incRow+j*incCol] = i*n+j+1;
        }
    }
}

void
printMatrix(size_t m, size_t n,
            const double *A,
            ptrdiff_t incRow, ptrdiff_t incCol)
{
    for (size_t i=0; i<m; ++i) {
        for (size_t j=0; j<n; ++j) {
            printf("%10.3lf", A[i*incRow+j*incCol]);
        }
        printf("\n");
    }
    printf("\n");
}

#ifndef MAX_ROWS
#define MAX_ROWS 5000
#endif

#ifndef MAX_COLS
#define MAX_COLS 5000
#endif


int
main()
{
    double *A = (double *) malloc(MAX_ROWS*MAX_COLS*sizeof(double));

    printf("%6s %6s ", "#m", "n");
    printf("%12s ", "t (col major)");
    printf("%12s ", "t (row major)");
    printf("\n");

    for (size_t m=256, n=256; m<=MAX_ROWS && n<=MAX_COLS; m+=16, n+=16) {
        printf("%6zu %6zu ", m, n);

        size_t incRow, incCol;
        double t0, t;

        // Store A col major
        incRow = 1;
        incCol = m;
        t0 = walltime();
        initMatrix(m, n, A, incRow, incCol);
        t = walltime() - t0;

        printf("%12.2lf ", t);

        // Store A row major
        incRow = n;
        incCol = 1;
        t0 = walltime();
        initMatrix(m, n, A, incRow, incCol);
        t = walltime() - t0;
        printf("%12.2lf ", t);

        printf("\n");
    }

    free(A);

    return 0;
}

set terminal svg size 900, 500
set output "bench.svg"
set xlabel "Matrix Dimensions (m=n)"
set ylabel "Time elapsed"
set title "Matrix Initialization"
set key outside
set pointsize 0.5
plot "bench.dat" using 1:3 with linespoints lt 2 lw 3 title "col major", \
     "bench.dat" using 1:4 with linespoints lt 3 lw 3 title "row major"