how to find the “true” entropy of std::random_device?

Question

I want to check whether my implementation of std::random_device has non-zero entropy (i.e. is non-deterministic), using std::random_device::entropy()

Answer 1

Entropy as a scientific term is misused when describing random numbers. Complexity might be a better term. Entropy in physics is defined as the logarithm of the number of available quantum states (not useful in RNG), and entropy in information theory is defined by the Shannon entropy, but that is geared towards the other extreme - how to put as much information into a noisy bit stream, not how to minimize the information.

For example, the digits of Pi look random, but the actual entropy of the digits is zero once you know that they derive from Pi. Increasing "Entropy" in RNG is basically a question of making the source of the numbers as obscure as possible.