Exp

Defined in header <cmath>.

Description

Computes 2 raised to the given power num.
The library provides overloads of std::exp2 for all cv-unqualified floating-point types as the type of the parameter num

Declarations

C++23

// 1)
/* floating-point-type */ exp2( /* floating-point-type */ num );
// 2)
float exp2f( float num  );
// 3)
long double exp2l( long double num );

Additional Overloads

// 4)
template< class Integer >
double exp2 ( Integer num );

C++11

// 1)
float exp2 ( float num );
// 2)
double exp2 ( double num );
// 3)
long double exp2 ( long double num );
// 4)
float exp2f( float num  );
// 5)
long double exp2l( long double num );

Additional Overloads

// 6)
template< class Integer >
double exp2 ( Integer num );

Parameters

​num - floating-point or integer value

Return value

If no errors occur, the base-2 exponential of num is returned.

If a range error due to overflow occurs, +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL is returned.

If a range error occurs due to underflow, 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):

If the argument is ±0, 1 is returned If the argument is -∞, +0 is returned If the argument is +∞, +∞ is returned If the argument is NaN, NaN is returned

Notes

The additional overloads are not required to be provided exactly as Additional Overloads. They only need to be sufficient to ensure that for their argument num of integer type, std::exp2(num) has the same effect as std::exp2(static_cast<double>(num)).

Examples

#include <cerrno>
#include <cfenv>
#include <cmath>
#include <cstring>
#include <iostream>
 
// #pragma STDC FENV_ACCESS ON
 
int main()
{
    std::cout 
        << "exp2(4) = " 
        << std::exp2(4) << '\n'
        << "exp2(0.5) = " 
        << std::exp2(0.5) << '\n'
        << "exp2(-4) = " 
        << std::exp2(-4) << '\n';
 
    // special values
    std::cout 
        << "exp2(-0) = " 
        << std::exp2(-0.0) << '\n'
        << "exp2(-Inf) = " 
        << std::exp2(-INFINITY) << '\n';
 
    // error handling
    errno = 0;
    std::feclearexcept(FE_ALL_EXCEPT);
 
    std::cout 
        << "exp2(1024) = " 
        << std::exp2(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 Result

exp2(4) = 16
exp2(0.5) = 1.41421
exp2(-4) = 0.0625
exp2(-0) = 1
exp2(-Inf) = 0
exp2(1024) = inf
errno == ERANGE: Numerical result out of range
FE_OVERFLOW raised