std::frexp,std::frexpf,std::frexpl(3)

NAME
std::frexp,std::frexpf,std::frexpl - std::frexp,std::frexpf,std::frexpl

Synopsis
   Defined in header <cmath>
   float frexp ( float arg, int* exp ); (1) (constexpr since C++23)
   float frexpf( float arg, int* exp ); (2) (since C++11)
                        (constexpr since C++23)
   double frexp ( double arg, int* exp ); (3) (constexpr since C++23)
   long double frexp ( long double arg, int* exp ); (4) (constexpr since C++23)
   long double frexpl( long double arg, int* exp ); (5) (since C++11)
                        (constexpr since C++23)
   double frexp ( IntegralType arg, int* exp ); (6) (since C++11)
                        (constexpr since C++23)
   1-5) Decomposes given floating point value arg into a normalized fraction and an
   integral power of two.
   6) A set of overloads or a function template accepting an argument of any integral
   type. Equivalent to (3) (the argument is cast to double).

Parameters
   arg - floating point value
   exp - pointer to integer value to store the exponent to

Return value
   If arg is zero, returns zero and stores zero in *exp.
   Otherwise (if arg is not zero), if no errors occur, returns the value x in the range
   (-1;-0.5], [0.5; 1) and stores an integer value in *exp such that x×2(*exp)
   == arg
   If the value to be stored in *exp is outside the range of int, the behavior is
   unspecified.
   If arg is not a floating-point number, the behavior is unspecified.

Error handling
   This function is not subject to any errors specified in math_errhandling.
   If the implementation supports IEEE floating-point arithmetic (IEC 60559),
     * If arg is ±0, it is returned, unmodified, and 0 is stored in *exp.
     * If arg is ±∞, it is returned, and an unspecified value is stored in *exp.
     * If arg is NaN, NaN is returned, and an unspecified value is stored in *exp.
     * No floating-point exceptions are raised.
     * If FLT_RADIX is 2 (or a power of 2), the returned value is exact, the current
       rounding mode is ignored

Notes
   On a binary system (where FLT_RADIX is 2), frexp may be implemented as
 {
     *exp = (value == 0) ? 0 : (int)(1 + std::logb(value));
     return std::scalbn(value, -(*exp));
 }
   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.

Example
   Compares different floating-point decomposition functions // Run this code
 #include <iostream>
 #include <cmath>
 #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';
 }

Possible output:
 Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,
 modf() makes 123 + 0.45
 frexp() makes 0.964453 * 2^7
 logb()/ilogb() make 1.92891 * 2^6

See also
   ldexp
   ldexpf multiplies a number by 2 raised to a power
   ldexpl (function)
   (C++11)
   (C++11)
   logb
   logbf
   logbl extracts exponent of the number
   (C++11) (function)
   (C++11)
   (C++11)
   ilogb
   ilogbf
   ilogbl extracts exponent of the number
   (C++11) (function)
   (C++11)
   (C++11)
   modf
   modff decomposes a number into integer and fractional parts
   modfl (function)
   (C++11)
   (C++11)