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>
   int exponent
   float scalbn ( float num, int exp );
   double scalbn ( double num, int exp (since C++11)
   ); (until C++23)
   long double scalbn ( long double num, int
   exp );
   constexpr /* floating-point-type */
               scalbn ( /* (since C++23)
   floating-point-type */ num, int exp );
                        (since C++11)
   float scalbnf( float num, int exp ); (2) (constexpr since
                        C++23)
   long double scalbnl( long double num, int (since C++11)
   exp ); (3) (constexpr since
                        C++23)
   long exponent
   float scalbln ( float num, long exp
   );
   double scalbln ( double num, long exp (1) (since C++11)
   ); (until C++23)
   long double scalbln ( long double num,
   long exp );
   constexpr /* floating-point-type */
               scalbln ( /* (since C++23)
   floating-point-type */ num, long exp );
   float scalblnf( float num, long exp (since C++11)
   ); (4) (5) (constexpr since
                        C++23)
   long double scalblnl( long double num, (since C++11)
   long exp ); (6) (constexpr since
                        C++23)
   Additional overloads
   Defined in header <cmath>
   template< class Integer > (since C++11)
   double scalbn( Integer num, int exp ); (A) (constexpr since
                        C++23)
   template< class Integer > (since C++11)
   double scalbln( Integer num, long exp ); (B) (constexpr since
                        C++23)
   1-6) Multiplies a floating point value num by FLT_RADIX raised to power exp.
   The library provides overloads of std::scalbn and std::scalbln for all
   cv-unqualified floating-point types as the type of the parameter num.
   (since C++23)
   A,B) Additional overloads are provided for all integer types, which are treated as
   double.

Parameters
   num - floating-point or integer value
   exp - integer value

Return value
   If no errors occur, num multiplied by FLT_RADIX to the power of exp
   (num×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 num is ±0, it is returned, unmodified.
     * If num is ±∞, it is returned, unmodified.
     * If exp is 0, then num is returned, unmodified.
     * If num 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 std::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.
   The additional overloads are not required to be provided exactly as (A,B). They only
   need to be sufficient to ensure that for their argument num of integer type:
     * std::scalbn(num, exp) has the same effect as
       std::scalbn(static_cast<double>(num), exp).
     * std::scalbln(num, exp) has the same effect as
       std::scalbln(static_cast<double>(num), exp).

Example
// Run this code
 #include <cerrno>
 #include <cfenv>
 #include <cmath>
 #include <cstring>
 #include <iostream>
 // #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 base-2 exponent
   frexpl (function)
   (C++11)
   (C++11)
   ldexp
   ldexpf multiplies a number by 2 raised to an integral power
   ldexpl (function)
   (C++11)
   (C++11)
   C documentation for
   scalbn