Suggested example for PER.4

CppCoreGuidelines.md

@@ -9116,6 +9116,27 @@ If your program spends most of its time waiting for the web or for a human, opti
 
 Simple code can be very fast. Optimizers sometimes do marvels with simple code
 
+##### Example, good
+
+    // clear expression of intent, fast execution
+    
+    vector v(100000);
+    
+    for(auto& c : v)
+        c = ~c;
+
+##### Example, bad
+
+    // intended to be faster, but is actually slower
+    
+    vector v(100000);
+    
+    for(size_t i=0; i<v.size(); i+=sizeof(uint64_t))
+    {
+        uint64_t& quad_word = *reinterpret_cast<uint64_t*>(&v[i]);
+        quad_word = ~quad_word;
+    }
+
 ##### Note
 
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