std::scalbn, std::scalbnf, std::scalbnl, std::scalbln, std::scalblnf, std::scalblnl
| Defined in header <cmath>
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| int exponent |
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| (1) | ||
float scalbn ( float num, int exp ); double scalbn ( double num, int exp ); |
(since C++11) (until C++23) |
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| 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 |
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| (4) | ||
float scalbln ( float num, long exp ); double scalbln ( double num, long exp ); |
(since C++11) (until C++23) |
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| 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) |
| Defined in header <cmath>
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| 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 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 <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[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
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