Guys, a logarithm is an abstract concept, not some math function.
You get a thing called a "base change". In this case we're dealing with a change of base of an element from some position in a finite field (private keys) to an element in the same position in a finite group (EC public keys) and the problem is to solve for the position without a way to go back from the latter to the first (which is assumed to be hard, but not yet proven). And this in the best case that we even have such an element, and not some fingerprint of it (an address), which makes the problem levels of more absurdly difficult. WTF is with the real numbers field log2 discussion, it makes no sense, we already know the ranges double in size at each step, of course any polynomial regression or whatever is a straight line. Dividing 1 by (2**64) is four levels of magnitude below a double-precision IEEE floating point, so what errors do you expect, they will always be after the 64-th zero decimal digit in reality. Nevermind the fact that there's an infinity of real numbers between any two real numbers, so an infinity of computations. Take 7 as a private key and try to solve back from [1/4, 1/8) interval, mission impossible.
This is not an analytical problem, it's a group theory problem.
log2 - It's just a way of representing numbers in a different way. I'll ask you again, do you know what you're talking about?
Number: 7
Representing 7 in different ways:
Base 10: 7
Base 2: 0111
Base 7: 10
Base 16: 0x07
Base 1:
Shall I go on?
Logarithm of 7 in the infinite field of real numbers:
Base 2: 2.8073549221... (infinite number of decimals) - it counts how many bits you need to represent value 7
Base e: 1.9459101490553132... (infinite number of decimals) - it counts how many natural numbers you need that, raised to this power, yields 7
Logarithm of 7 in some modular finite field with N = 3:
log(7) = mod 3 (oh no, this doesn't work, hmm... is it 0? 1? 2? damn, something is missing, maybe we didn't even define the neutral element yet? or not even an binary addition operator?)
So, do YOU know what you are talking about?