On the other hand, this inline assembly meshes very well with the register allocator and instruction scheduler in modern compilers. So it's perfect for teachin

On the other hand, this inline assembly meshes very well with the register allocator and instruction scheduler in modern compilers. So it's perfect for teaching the compiler about the few special purpose instructions it doesn't know about without compromising the performance of the rest of the code. The one in the parent comment does not; it's basically a black box and the compiler has to save and restore the entire state of the function around it. Total performance killer unless you write large chunks of code in inline assembly (and then you're probably better off just using an assembly file).