Namespaces
Variants

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

From cppreference.net
C++
Numerics library
Common mathematical functions
Nearest integer floating point operations
(C++11)
(C++11)
(C++11) (C++11) (C++11)
Floating point manipulation functions
(C++11) (C++11)
(C++11)
(C++11)
Classification and comparison
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Types
(C++11)
(C++11)
(C++11)
Macro constants
Defined in header <cmath>
(1)
float exp2 ( float num ) ;

double exp2 ( double num ) ;

long double exp2 ( long double num ) ;
(until C++23)
/*floating-point-type*/
exp2 ( /*floating-point-type*/ num ) ;
(since C++23)
(constexpr since C++26)
float exp2f ( float num ) ;
(2) (since C++11)
(constexpr since C++26)
long double exp2l ( long double num ) ;
(3) (since C++11)
(constexpr since C++26)
SIMD overload (since C++26)
Defined in header <simd>
template < /*math-floating-point*/ V >

constexpr /*deduced-simd-t*/ < V >

exp2 ( const V & v_num ) ;
(S) (since C++26)
Defined in header <cmath>
template < class Integer >
double exp2 ( Integer num ) ;
(A) (constexpr since C++26)
1-3) 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. (since C++23)
S) The SIMD overload performs an element-wise std::exp2 on v_num .
(See math-floating-point and deduced-simd-t for their definitions.)
(since C++26)
A) Additional overloads are provided for all integer types, which are treated as double .
(since C++11)

Contents

Parameters

num - floating-point or integer value

Return value

If no errors occur, the base- 2 exponential of num ( 2 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 (A) . 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 ) ) .

For integral exponents, it may be preferable to use std::ldexp .

Example

Run this code 
#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);
    const double inf = std::exp2(1024);
    const bool is_range_error = errno == ERANGE;
    std::cout << "exp2(1024) = " << inf << '\n';
    if (is_range_error)
        std::cout << "    errno == ERANGE: " << std::strerror(ERANGE) << '\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 ( e x )
(function)
(C++11) (C++11) (C++11)
returns e raised to the given power, minus 1 ( e x -1 )
(function)
(C++11) (C++11)
multiplies a number by 2 raised to an integral power
(function)
(C++11) (C++11) (C++11)
base 2 logarithm of the given number ( log 2 (x) )
(function)
C documentation for exp2