[JadeNB]

> Time taken to execute the function fib(a) is denoted by t(a).

This function has a name: t(a) = fib(a) (up to some fiddling with constants, depending on how you count execution 'time').

[NAFV_P]

> This function has a name: t(a) = fib(a) (up to some fiddling with constants, depending on how you count execution 'time').

I was thinking of either time() or gettimeofday() from the standard and POSIX libraries respectively.