Other Alias

exp2, exp2l## SYNOPSIS

**#include <math.h>
**

double exp2(double *x***);
float exp2f(float**

*x*

**);**

long double exp2l(long double

long double exp2l(long double

*x*

**);**

## DESCRIPTION

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 2***x*.

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, and is not representable, a range error may occur, and either 0.0 (if supported), or an implementation-defined value shall be returned.

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.

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

For IEEE Std 754-1985 **double**, 1024 <= *x* implies *exp2*(
*x*) has overflowed. The value
*x* < -1022 implies *exp*( *x*) has underflowed.

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.

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .