The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> exp2, exp2f, exp2l - exponential base 2 functions

#### SYNOPSIS

> ``#include <math.h>
> double exp2(double` x`);
> float exp2f(float` x`);
> long double exp2l(long double` x`);
> ``

#### DESCRIPTION

> [CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

> These functions shall compute the base-2 exponential of x.

> An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

#### RETURN VALUE

> Upon successful completion, these functions shall return 2x.

> If the correct value would cause overflow, a range error shall occur and exp2(), exp2f(), and exp2l() shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.

> If the correct value would cause underflow, [MXX] and is not representable, a range error may occur, and exp2(), exp2f(), and exp2l() shall return [MXX] 0.0, or (if the IEC 60559 Floating-Point option is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

> [MX] If x is NaN, a NaN shall be returned.

> If x is ±0, 1 shall be returned.

> If x is -Inf, +0 shall be returned.

> If x is +Inf, x shall be returned.

> [MXX] If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.

#### ERRORS

> These functions shall fail if:

> Range Error
>   The result overflows.

>   If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.

> These functions may fail if:

> Range Error
>   The result underflows.

>   If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> exp, feclearexcept, fetestexcept, isnan, log

> XBD Treatment of Error Conditions for Mathematical Functions, <math.h>

#### CHANGE HISTORY

> First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

#### Issue 7

> POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0108 [68] and XSH/TC1-2008/0109 [68] are applied.

> POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0102 [630] is applied.

End of informative text.

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