std::scalbn, std::scalbnf, std::scalbnl, std::scalbln, std::scalblnf, std::scalblnl
Defined in header <cmath> | ||
int exponent | ||
| (1) | ||
float scalbn (float num, int exp ); double scalbn (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) |
longdouble scalbnl(longdouble 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 ); | (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) |
longdouble scalblnl(longdouble num, long exp ); | (6) | (since C++11) (constexpr since C++23) |
Defined in header <cmath> | ||
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) |
std::scalbn and std::scalbln for all cv-unqualified floating-point types as the type of the parameter num.(since C++23)Contents |
[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 longdouble, 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 <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 valuesstd::cout<<"scalbn(-0, 10) = "<< std::scalbn(-0.0, 10)<<'\n'<<"scalbn(-Inf, -1) = "<< std::scalbn(-INFINITY, -1)<<'\n'; // error handlingerrno=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
[edit]See also
(C++11)(C++11) | decomposes a number into significand and base-2 exponent (function) |
(C++11)(C++11) | multiplies a number by 2 raised to an integral power (function) |
C documentation for scalbn | |
