Question

I am using the following code to divide all int array elements with constant factor using SSE.

void sse_div(int *arr,int num_shift,int N) // devide all array elements by 2
{
         num_shift=1;
     int nb_iters = N / 4;    
     __declspec(align(32))int *a1=arr;

      __m128i* l = (__m128i*)a1;  
     for (int i = 0; i < nb_iters; ++i, ++l)
          _mm_store_si128( l, _mm_srai_epi32(*l,num_shift)); //Error line

}

But I am getting the following error

I am unable to get rid of this problem.
Can anybody please help to solve this problem.
Any help will be appreciated.

Thanks in Advance

Answer 1

Since your input array is apparently misaligned you can use unaligned loads/stores, e.g.:

void sse_div(int *arr, int N)     // divide all array elements by 2
{
    for (int i = 0; i < nb_iters; i += 4)
    {
        __m128i v = _mm_loadu_si128(&arr[i]);
        v = _mm_srai_epi32(v, 1);
        _mm_storeu_si128(&arr[i], v);
    }
}

Note that there may be a significant performance hit from using unaligned loads/stores (depending on what CPU you are running on), so if possible you should make your arr array 16 byte aligned when you allocate the memory.