std::scalbn,std::scalbnf,std::scalbnl,std::scalbln,std::scalblnf,std::scalblnl(3)

NAME
std::scalbn,std::scalbnf,std::scalbnl,std::scalbln,std::scalblnf,std::scalblnl - std::scalbn,std::scalbnf,std::scalbnl,std::scalbln,std::scalblnf,std::scalblnl

Synopsis
   Defined in header <cmath>
   float scalbn ( float x, int exp ); (1) (since C++11)
                        (constexpr since C++23)
   float scalbnf( float x, int exp ); (2) (since C++11)
                        (constexpr since C++23)
   double scalbn ( double x, int exp ); (3) (since C++11)
                        (constexpr since C++23)
   long double scalbn ( long double x, int exp ); (4) (since C++11)
                        (constexpr since C++23)
   long double scalbnl( long double x, int exp ); (5) (since C++11)
                        (constexpr since C++23)
   double scalbn ( IntegralType x, int exp ); (6) (since C++11)
                        (constexpr since C++23)
   float scalbln ( float x, long exp ); (7) (since C++11)
                        (constexpr since C++23)
   float scalblnf( float x, long exp ); (8) (since C++11)
                        (constexpr since C++23)
   double scalbln ( double x, long exp ); (9) (since C++11)
                        (constexpr since C++23)
   long double scalbln ( long double x, long exp ); (10) (since C++11)
                        (constexpr since C++23)
   long double scalblnl( long double x, long exp ); (11) (since C++11)
                        (constexpr since C++23)
   double scalbln ( IntegralType x, long exp ); (12) (since C++11)
                        (constexpr since C++23)
   1-5,7-11) Multiplies a floating point value x by FLT_RADIX raised to power exp.
   6,12) A set of overloads or a function template accepting an argument of any
   integral type. Equivalent to (3) or (9) (the argument is cast to double).

Parameters
   x - floating point value
   exp - integer value

Return value
   If no errors occur, x multiplied by FLT_RADIX to the power of arg (x×FLT_RADIXexp
   ) is returned.
   If a range error due to overflow occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is
   returned.
   If a range error due to underflow occurs, the correct result (after rounding) is
   returned.

Error handling
   Errors are reported as specified in math_errhandling
   If the implementation supports IEEE floating-point arithmetic (IEC 60559),
     * Unless a range error occurs, FE_INEXACT is never raised (the result is exact)
     * Unless a range error occurs, the current rounding mode is ignored
     * If x is ±0, it is returned, unmodified
     * If x is ±∞, it is returned, unmodified
     * If exp is 0, then x is returned, unmodified
     * If x is NaN, NaN is returned

Notes
   On binary systems (where FLT_RADIX is 2), std::scalbn is equivalent to std::ldexp.
   Although std::scalbn and std::scalbln are specified to perform the operation
   efficiently, on many implementations they are less efficient than multiplication or
   division by a power of two using arithmetic operators.
   The function name stands for "new scalb", where scalb was an older non-standard
   function whose second argument had floating-point type.
   The scalbln function is provided because the factor required to scale from the
   smallest positive floating-point value to the largest finite one may be greater than
   32767, the standard-guaranteed INT_MAX. In particular, for the 80-bit long double,
   the factor is 32828.
   The GNU implementation does not set errno regardless of math_errhandling

Example
// Run this code
 #include <iostream>
 #include <cmath>
 #include <cerrno>
 #include <cstring>
 #include <cfenv>
 // #pragma STDC FENV_ACCESS ON
 int main()
 {
     std::cout << "scalbn(7, -4) = " << std::scalbn(7, -4) << '\n'
               << "scalbn(1, -1074) = " << std::scalbn(1, -1074)
               << " (minimum positive subnormal double)\n"
               << "scalbn(nextafter(1,0), 1024) = "
               << std::scalbn(std::nextafter(1,0), 1024)
               << " (largest finite double)\n";
     // special values
     std::cout << "scalbn(-0, 10) = " << std::scalbn(-0.0, 10) << '\n'
               << "scalbn(-Inf, -1) = " << std::scalbn(-INFINITY, -1) << '\n';
     // error handling
     errno = 0;
     std::feclearexcept(FE_ALL_EXCEPT);
     std::cout << "scalbn(1, 1024) = " << std::scalbn(1, 1024) << '\n';
     if (errno == ERANGE)
         std::cout << " errno == ERANGE: " << std::strerror(errno) << '\n';
     if (std::fetestexcept(FE_OVERFLOW))
         std::cout << " FE_OVERFLOW raised\n";
 }

Possible output:
 scalbn(7, -4) = 0.4375
 scalbn(1, -1074) = 4.94066e-324 (minimum positive subnormal double)
 scalbn(nextafter(1,0), 1024) = 1.79769e+308 (largest finite double)
 scalbn(-0, 10) = -0
 scalbn(-Inf, -1) = -inf
 scalbn(1, 1024) = inf
     errno == ERANGE: Numerical result out of range
     FE_OVERFLOW raised

See also
   frexp
   frexpf decomposes a number into significand and a power of 2
   frexpl (function)
   (C++11)
   (C++11)
   ldexp
   ldexpf multiplies a number by 2 raised to a power
   ldexpl (function)
   (C++11)
   (C++11)