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

 

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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)

Parameters

num

-

floating-point or integer value

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.

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

expexpfexpl (C++11)(C++11)	returns e raised to the given power (\({\small e^x}\)ex) (function)
expm1expm1fexpm1l (C++11)(C++11)(C++11)	returns e raised to the given power, minus one (\({\small e^x-1}\)ex-1) (function)
ldexpldexpfldexpl (C++11)(C++11)	multiplies a number by 2 raised to an integral power (function)
log2log2flog2l (C++11)(C++11)(C++11)	base 2 logarithm of the given number (\({\small\log_{2}{x}}\)log2(x)) (function)
C documentation for exp2