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

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

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)
float scalbnf( float x, int exp );
double scalbn ( double x, int exp ); (2) (since C++11)
long double scalbn ( long double x, int exp ); (3) (since C++11)
long double scalbnl( long double x, int exp );
double scalbn ( IntegralType x, int exp ); (4) (since C++11)
float scalbln ( float x, long exp ); (5) (since C++11)
float scalblnf( float x, long exp );
double scalbln ( double x, long exp ); (6) (since C++11)
long double scalbln ( long double x, long exp ); (7) (since C++11)
long double scalblnl( long double x, long exp );
double scalbln ( IntegralType x, long exp ); (8) (since C++11)

1-3,5-7) Multiplies a floating point value x by FLT_RADIX raised to power exp.
4,8) A set of overloads or a function template accepting an argument of any integral_type. Equivalent to (2) or (6) (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