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# std::exp2

From cppreference.com
< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
double exp2( double n ); | (1) | (since C++11)
float exp2( float n ); | (2) | (since C++11)
long double exp2( long double n ); | (3) | (since C++11)
double exp2( Integral 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 (1) (the argument is cast to double).

### [edit] Parameters

n | - | value of floating-point or Integral type

### [edit] 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.

### [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] Example

Run this code

    #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

### [edit] See also

exp | returns e raised to the given power (ex) (function) [edit]
expm1 (C++11) | returns e raised to the given power, minus one (ex-1) (function) [edit]
log2 (C++11) | base 2 logarithm of the given number (log2(x)) (function) [edit]
C documentation for exp2

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