To make a better comparison, you should strftimeLookup
do a getMonthNumber as well. Now it's the only
case that isn't penalized by an extra subroutine call. Or
you could eliminate the call from all cases, the lookup time
won't be different depending on the number of the month.
Just use a fixed month number (but don't hardcode it as a
literal, or else the compiler might pre-calculate some
calculations).