c - How to dynamically allocate 2d array that's 16B aligned

Question

I'd like to allocate 2D array (square matrix) using memalign with 16B instead of using just malloc.

I have

A =(float **) malloc( (*dim) * sizeof(float*));
for ( i = 0 ; i < (*dim) ; i++) {

    A[i] = (float*) malloc(sizeof(float)*(*dim));
}

how can I change code above with memalign.

Answer 1

With malloc() you need to request 15 extra bytes and then round-up the returned pointer to the nearest multiple of 16, e.g.:

void* p = malloc(size + 15);
void* paligned;
if (!p) { /* handle errors */ }
paligned = (void*)(((size_t)p + 15) / 16 * 16);
/* use paligned */
free(p);