IEEE Std 1003.1-2008

Copyright © 2001-2008 The IEEE and The Open Group

exp2, exp2f, exp2l - exponential base 2 functions

#include <math.h>

double exp2(doublex);

float exp2f(floatx);

long double exp2l(long doublex);

^{[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

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return 2

.^{x}If the correct value would cause overflow, a range error shall occur and

exp2(),exp2f(), andexp2l() 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

^{[MX]}either 0.0 (if supported), or an implementation-defined value shall be returned.

^{[MX]}Ifxis NaN, a NaN shall be returned.If

xis ±0, 1 shall be returned.If

xis -Inf, +0 shall be returned.If

xis +Inf,xshall be returned.If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.

These functions shall fail if:

- Range Error
- The result overflows.
If the integer expression (

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

None.

For IEEE Std 754-1985

double, 1024 <=ximpliesexp2(x) has overflowed. The valuex< -1022 impliesexp(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.

None.

None.

exp,feclearexcept,fetestexcept,isnan,logXBD

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

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

return to top of page

POSIX ® is a registered Trademark of The IEEE.

Copyright © 2001-2008 The IEEE and The Open Group, All Rights Reserved

[ Main Index | XBD | XSH | XCU | XRAT ]