 <p>If you use the Intel C compiler, and set sufficiently high optimisation options, you will find that some of your loops get 'vectorised', which means the compiler has rewritten them to use SSE-style instructions.</p> <p>If you want to use SSE operations directly, you use the intrinsics defined in the 'xmmintrin.h' header file; say</p> <p>#include &lt;xmmintrin.h&gt;</p> <p>__m128 U, V, W; float ww[4];</p> <p>V=_mm_set1_ps(1.5);</p> <p>U=_mm_set_ps(0,1,2,3);</p> <p>W=_mm_add_ps(U,V);</p> <p>_mm_storeu_ps(ww,W);</p>