std::frexp, std::frexpf, std::frexpl

Since C++23

Header: <cmath>

1-3) Decomposes given floating point value num into a normalized fraction and an integral exponent of two.The library provides overloads of std::frexp for all cv-unqualified floating-point types as the type of the parameter num.(since C++23)

# Declarations

float frexp ( float num, int* exp );
double frexp ( double num, int* exp );
long double frexp ( long double num, int* exp );

(until C++23)

constexpr /* floating-point-type */
frexp ( /* floating-point-type */ num, int* exp );

(since C++23)

float frexpf( float num, int* exp );

(since C++11) (constexpr since C++23)

long double frexpl( long double num, int* exp );

(since C++11) (constexpr since C++23)

Additional overloads (since C++11)

template< class Integer >
double frexp ( Integer num, int* exp );

(constexpr since C++23)

# Parameters

num: floating-point or integer value
exp: pointer to integer value to store the exponent to

# Return value

If num is zero, returns zero and stores zero in *exp.

# Notes

On a binary system (where FLT_RADIX is 2), std::frexp may be implemented as

The function std::frexp, together with its dual, std::ldexp, can be used to manipulate the representation of a floating-point number without direct bit manipulations.

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::frexp(num, exp) has the same effect as std::frexp(static_cast(num), exp).

# Example

#include <cmath>
#include <iostream>
#include <limits>
 
int main()
{
    double f = 123.45;
    std::cout << "Given the number " << f << " or " << std::hexfloat
              << f << std::defaultfloat << " in hex,\n";
 
    double f3;
    double f2 = std::modf(f, &f3);
    std::cout << "modf() makes " << f3 << " + " << f2 << '\n';
 
    int i;
    f2 = std::frexp(f, &i);
    std::cout << "frexp() makes " << f2 << " * 2^" << i << '\n';
 
    i = std::ilogb(f);
    std::cout << "logb()/ilogb() make " << f / std::scalbn(1.0, i)
              << " * " << std::numeric_limits<double>::radix
              << "^" << std::ilogb(f) << '\n';
}