std::scalbn, std::scalbnf, std::scalbnl, std::scalbln, std::scalblnf, std::scalblnl (original) (raw)

Defined in header
int exponent
(1)
float scalbn ( float num, int exp ); double scalbn ( double num, int exp ); long double scalbn ( long double num, int exp );		(since C++11) (until C++23)
constexpr /* floating-point-type / scalbn ( / floating-point-type */ num, int exp );		(since C++23)
float scalbnf( float num, int exp );	(2)	(since C++11) (constexpr since C++23)
long double scalbnl( long double num, int exp );	(3)	(since C++11) (constexpr since C++23)
long exponent
(4)
float scalbln ( float num, long exp ); double scalbln ( double num, long exp ); long double scalbln ( long double num, long exp );		(since C++11) (until C++23)
constexpr /* floating-point-type / scalbln ( / floating-point-type */ num, long exp );		(since C++23)
float scalblnf( float num, long exp );	(5)	(since C++11) (constexpr since C++23)
long double scalblnl( long double num, long exp );	(6)	(since C++11) (constexpr since C++23)
Additional overloads
Defined in header
template< class Integer > double scalbn( Integer num, int exp );	(A)	(since C++11) (constexpr since C++23)
template< class Integer > double scalbln( Integer num, long exp );	(B)	(since C++11) (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.

[edit] Parameters

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

[edit] 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.

[edit] 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.

[edit] 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).

[edit] Example

#include #include #include #include #include // #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: