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std::random_device::entropy

From cppreference.com
< cpp‎ | numeric‎ | random‎ | random device
 
 
 
 
 
double entropy() const;
(since C++11)

Obtains an estimate of the random number device entropy, which is a floating-point value between 0 and log
2
(max()+1)
(which is equal to std::numeric_limits<unsigned int>::digits). If the device has n states whose individual probabilities are P
0
,...,P
n-1
, the device entropy S is defined as

S = -Σn-1
i=0
P
i
log(P
i
)

A deterministic random number generator (e.g. a pseudo-random engine) has entropy zero.

Contents

[edit] Exceptions

noexcept specification:  
noexcept
  

[edit] Return value

The value of the device entropy, or zero if not applicable.

[edit] Notes

This function is not fully implemented in some standard libraries. For example, GNU libstdc++ and LLVM libc++ always return zero even though the device is non-deterministic. In comparison, Microsoft Visual C++ implementation always returns 32, and boost.random returns 10.

[edit] Example

Example output on one of the implementations

#include <iostream>
#include <random>
 
int main()
{
    std::random_device rd;
    std::cout << rd.entropy() << '\n';
}

Possible output:

32