mat4_1.cpp

struct mat4
{
  union alignas(16)
  {
    struct
    {
      float
        a, b, c, d,
        e, f, g, h,
        i, j, k, l,
        m, n, o, p;
    };
    float data[16];
    // This is the important data.
    __m128 sse_data[4];
  };
};

// or a more "clean" implementation
struct mat4
{
    __m128 data[4];
};