how is strcmp implemented so efficiently?

[Reza Roboubi <reza@xxxxxxxxxx>]

I noticed that strcmp is extremely smart.  It knows when one parameter 
has constant length, determined at compile time.  In that case it 
reverts to an inline version of the x86 string commands.

I looked into the headers and strcmp is defined as an extern(not inline.)

How would I ever write such an efficient function?  Is it possible(even 
_with_ the use of asm?!)

Reza.