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
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.
SEE ALSO
exp() , feclearexcept() , fetestexcept() , isnan() , log() , the Base
Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of
Error Conditions for Mathematical Functions, <math.h>
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 .