How do you get bit_length() in PARI/GP

Question

I've looked on google and couldn't find the answer and thought i'd ask PARI/GP users here. My question is simply How do you get bit_length() in PARI/GP, that you can use at there interpreter here: https://pari.math.u-bordeaux.fr/gp.html

Answer 1

For integers, it is just bit_length(n) = #binary(n);. For example:

bit_length(n) = #binary(n);
bit_length(100)
> 7

Answer 2

Faster for large numbers than binary is just to use logint (requires n > 0).

1 + logint(n,2)

Answer 3

Probably the fastest way (for positive integers) is

len(n)=exponent(n)+1