How to determine how many bytes an integer needs?

Question

I\'m looking for the most efficient way to calculate the minimum number of bytes needed to store an integer without losing precision.

e.g.

int: 10 = 1 byte
         


        

Answer 1

There are already a lot of answers here, but if you know the number ahead of time, in c++ you can use a template to make use of the preprocessor.

template 
struct RequiredBytes {
    enum : int { value = 1 + (N > 255 ? RequiredBits<(N >> 8)>::value : 0) };
};

template <>
struct RequiredBytes<0> {
    enum : int { value = 1 };
};

const int REQUIRED_BYTES_18446744073709551615 = RequiredBytes<18446744073709551615>::value; // 8

or for a bits version:

template 
struct RequiredBits {
    enum : int { value = 1 + RequiredBits<(N >> 1)>::value };
};

template <>
struct RequiredBits<1> {
    enum : int { value = 1 };
};

template <>
struct RequiredBits<0> {
    enum : int { value = 1 };
};

const int REQUIRED_BITS_42 = RequiredBits<42>::value; // 6