What's a modern libc? Not being snide or anything: I have no idea. I didn't know where to look so I looked at glibc [1] and that, in fact, does seem to be how it works.
This might be the most delicious piece of code ever written ( I cannot judge that, really), but we're talking 2307 lines for a string comparison.
I'm impressed, but also scared and amused. I always look with envy at system level guys, lacking the knowledge to play on that level. This, though, comforts me quite a bit. That's just not my definition of 'fun'.
I've never written anything non-trival in C and even that was ages ago so I didn't hope to be able judge the niceties of different implementations but I can't even tell what the algorithm is in that one.