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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 andstd::scalbln for all cv-unqualified floating-point types as the type of the parameternum.(since C++23)Contents |
| num | - | floating-point or integer value |
| exp | - | integer value |
If no errors occur,num multiplied byFLT_RADIX to the power ofexp (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.
Errors are reported as specified inmath_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
On binary systems (whereFLT_RADIX is2),std::scalbn is equivalent tostd::ldexp.
Althoughstd::scalbn andstd::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", wherescalb was an older non-standard function whose second argument had floating-point type.
Thestd::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-guaranteedINT_MAX. In particular, for the 80-bitlongdouble, the factor is 32828.
The GNU implementation does not seterrno regardless ofmath_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 argumentnum of integer type:
#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) = 0.4375scalbn(1, -1074) = 4.94066e-324 (minimum positive subnormal double)scalbn(nextafter(1,0), 1024) = 1.79769e+308 (largest finite double)scalbn(-0, 10) = -0scalbn(-Inf, -1) = -infscalbn(1, 1024) = inf errno == ERANGE: Numerical result out of range FE_OVERFLOW raised
(C++11)(C++11) | decomposes a number into significand and base-2 exponent (function)[edit] |
(C++11)(C++11) | multiplies a number by2 raised to an integral power (function)[edit] |
C documentation forscalbn | |
