title: MMX SSE extensions for for loop
body: <p>I have GCC 9.2 compiler.
  If i use MMX or SSE/AVX extension you will have you code run in parallel, so it will be faster.
  How to tell the compiler to use this instructions
  I have a code snippet i want to parallel:</p>
  
  <pre><code>char max(char * a, int n){
      char max = (*a);
      for (int i = 0 ; i&lt; n ; ++i){
              if (max &lt; a[i]){
                  max = a[i];
              }
      }
      return max;
  }
  </code></pre>
  
  <p>it generates code using SSE extension but don't use pmaxub 
  why</p>