While the lack of error checking would certainly be foolish, you can micro-optimize this even more.
The while() loop isn't smart enough to compile down to a 'scasb' instruction, whereas if you use 'memchr', the compiler is smart enough to play some games with it. While I haven't checked the code strncpy() uses, I know for a fact that memcpy() will reduce to either a 'rep movsb' sequence, or more likely for only 8 bytes, 2 loads and 2 stores (4 instructions). If you're on an Alpha, it'll be 2 instructions, a single load and a single store.
strncpy() is portable and is good in that respect. memcpy() is less so, since it presumes certain things about the processor architecture.
/me is glad to see Ovid start hacking Inline::C. It's a lot of fun. Perl is good, but not always perfect. Perl combined with Inline::C can let you do some truly scarey things.