Example of POSIX memalign in C

array_alignment.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define SIZE 1000000


typedef struct {
    float *x;
} test_s;


void add(float * restrict a, float * restrict b, float * restrict c)
{
    size_t i;

    for (i = 0; i < SIZE; ++i) {
        c[i] = a[i] + b[i];
    }
}


int main()
{
    clock_t t0, tf;
    float *a = NULL, *b = NULL;
    float *Aa = NULL, *Ab = NULL;

    test_s *C, *AC;

    a = (float *)malloc(sizeof(float) * SIZE);
    b = (float *)malloc(sizeof(float) * SIZE);
    C = (test_s *)malloc(sizeof(test_s));
    C->x = (float *)malloc(SIZE * sizeof(float));

    posix_memalign((void *)&Aa, 128, SIZE * sizeof(float));
    posix_memalign((void *)&Ab, 128, SIZE * sizeof(float));
    posix_memalign((void *)&AC, 128, sizeof(test_s));
    posix_memalign((void *)&AC->x, 128, SIZE * sizeof(float));

    t0 = clock();
    add(a, b, C->x);
    tf = clock();
    printf("Non-aligned array: %lf\n", ((double)(tf - t0) / CLOCKS_PER_SEC));

    t0 = clock();
    add(Aa, Ab, AC->x);
    tf = clock();
    printf("Aligned array: %lf\n", ((double)(tf - t0) / CLOCKS_PER_SEC));

    free(a);
    free(b);
    free(Aa);
    free(Ab);
    free(C->x);
    free(C);
    free(AC->x);
    free(AC);

    return 0;
}