std::exp2, std::exp2f, std::exp2l

Defined in header <cmath> 
float       exp2 ( float n );
float       exp2f( float n );
 (1) (since C++11) 
double      exp2 ( double n );
 (2) (since C++11) 
long double exp2 ( long double n );
long double exp2l( long double n );
 (3) (since C++11) 
double      exp2 ( IntegralType n );
 (4) (since C++11)
1-3) Computes 2 raised to the given power n
4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to (2) (the argument is cast to double).

Parameters

n - value of floating-point or Integral type

Return value

If no errors occur, the base-2 exponential of n (2n
) 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

Example

#include <iostream>
#include <cmath>
#include <cerrno>
#include <cstring>
#include <cfenv>
#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 output:

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

See also

(C++11)(C++11)
 returns e raised to the given power (ex)
(function)
(C++11)(C++11)(C++11)
 returns e raised to the given power, minus one (ex-1)
(function)
(C++11)(C++11)(C++11)
 base 2 logarithm of the given number (log2(x))
(function)

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