add two avx instructions example & simple clear screen

avx/add.c

@@ -0,0 +1,32 @@
+/* Construct a 256-bit vector from 4 64-bit doubles. Add it to itself
+ * and print the result.
+ */
+
+#include <stdio.h>
+#include <immintrin.h>
+
+int main() {
+
+  __m256i hello;
+  // Construction from scalars or literals.
+  __m256d a = _mm256_set_pd(1.0, 2.0, 3.0, 4.0);
+
+  // Does GCC generate the correct mov, or (better yet) elide the copy
+  // and pass two of the same register into the add? Let's look at the assembly.
+  __m256d b = _mm256_set_pd(0.0, 0.0, 0.0, 0.0), c;
+for(int i = 0; i < 1000000000; ++i){
+  // Add the two vectors, interpreting the bits as 4 double-precision
+  // floats.
+  c = _mm256_add_pd(a, b);
+  b = c;
+  
+ }
+
+  // Do we ever touch DRAM or will these four be registers?
+  __attribute__ ((aligned (32))) double output[4];
+  _mm256_store_pd(output, c);
+
+  printf("%f %f %f %f\n",
+         output[0], output[1], output[2], output[3]);
+  return 0;
+}