Word length and number of bits in an integer

[Dirk Laurie <dirk.laurie@gmail.com>]

I need a routine for the exact smallest value B such that x>>B is zero,
where x is a t_INT.  SInce a may be very large indeed, I coded it thus:

{ bitsin(x) =
   my(w=32*(length(x)-1)); x>>=w;
      while(x, x>>=1; w+=1);
   w
}

I have two queries:

1. Am I missing some useful builtin function?
2. Can I rely on the words making up x to be 32-bit?
    If not, how do I find out the word length from inside GP?