Namespaces
Variants
Views
Actions

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

From cppreference.com
< cpp‎ | numeric‎ | math
 
 
 
Common mathematical functions
Functions
Basic operations
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)
Exponential functions
exp2
(C++11)
(C++11)
(C++11)
(C++11)
Power functions
(C++11)
(C++11)
Trigonometric and hyperbolic functions
(C++11)
(C++11)
(C++11)
Error and gamma functions
(C++11)
(C++11)
(C++11)
(C++11)
Nearest integer floating point operations
(C++11)(C++11)(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)
Floating point manipulation functions
(C++11)(C++11)
(C++11)
(C++11)
(C++11)(C++11)
(C++11)
Classification/Comparison
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Macro constants
(C++11)(C++11)(C++11)(C++11)(C++11)
 
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)
Additional overloads (since C++11)
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)
A) Additional overloads are provided for all integer types, which are treated as double.
(since C++11)

Contents

[edit] Parameters

num - floating-point or integer value

[edit] Return value

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

[edit] 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.

[edit] 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.

[edit] Example

#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

[edit] See also

(C++11)(C++11)
returns e raised to the given power (ex)
(function) [edit]
(C++11)(C++11)(C++11)
returns e raised to the given power, minus one (ex-1)
(function) [edit]
(C++11)(C++11)
multiplies a number by 2 raised to an integral power
(function) [edit]
(C++11)(C++11)(C++11)
base 2 logarithm of the given number (log2(x))
(function) [edit]