Not a compiler option, and it's not "set" to 15. randbits is supposed to show how many bits the c library function used to generate random numbers actually provides. So on WinXP using rand from the msvcrt library, you only get 15 (my recollection was that it was actually 14) bits. Note that this isn't a limitation of Windows; if someone were to go to the trouble of bundling a random number generator with perl,
there'd be no need to depend on whatever the c library dishes up.