NAME¶

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

Synopsis¶

Defined in header <cmath>
float exp2 ( float num );

double exp2 ( double num ); (until C++23)

long double exp2 ( long double num );
/* floating-point-type */ (since C++23)
exp2 ( /* floating-point-type */ num ); (constexpr since C++26)
float exp2f( float num ); (1) (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 > (A) (constexpr since C++26)
double exp2 ( Integer num );

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 (since C++11)
treated as double.

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¶

exp
expf returns e raised to the given power (\({\small e^x}\)e^x)
expl (function)
(C++11)
(C++11)
expm1
expm1f
expm1l returns e raised to the given power, minus one (\({\small e^x-1}\)e^x-1)
(C++11) (function)
(C++11)
(C++11)
ldexp
ldexpf multiplies a number by 2 raised to an integral power
ldexpl (function)
(C++11)
(C++11)
log2
log2f
log2l base 2 logarithm of the given number (\({\small\log_{2}{x}}\)log[2](x))
(C++11) (function)
(C++11)
(C++11)
C documentation for
exp2