Nice article. Emphasizes that the only way to know what's going on is to test and inspect the assembly.

I tried it, and without any flags gcc used 'sqrtsd' (the sse version) for me. -msse was enabled by default.. So I'm not sure that what he says about needing an obscure gcc flag, but i guess it depends on your distro.

I didn't know about the rsqrtss*x trick.. that's pretty cool.