.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "EXP2" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" exp2 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
exp2, exp2f, exp2l \- exponential base 2 functions
.SH SYNOPSIS
.LP
\fB#include <math.h>
.br
.sp
double exp2(double\fP \fIx\fP\fB);
.br
float exp2f(float\fP \fIx\fP\fB);
.br
long double exp2l(long double\fP \fIx\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
These functions shall compute the base-2 exponential of \fIx\fP.
.LP
An application wishing to check for error situations should set \fIerrno\fP
to zero and call
\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
On return, if \fIerrno\fP is non-zero or
\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.
.SH RETURN VALUE
.LP
Upon successful completion, these functions shall return 2\fI**x\fP.
.LP
If the correct value would cause overflow, a range error shall occur
and \fIexp2\fP(), \fIexp2f\fP(), and \fIexp2l\fP() shall
return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL,
respectively.
.LP
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.
.LP
If
\fIx\fP is NaN, a NaN shall be returned.
.LP
If \fIx\fP is \(+-0, 1 shall be returned.
.LP
If \fIx\fP is -Inf, +0 shall be returned.
.LP
If \fIx\fP is +Inf, \fIx\fP shall be returned.
.LP
If the correct value would cause underflow, and is representable,
a range error may occur and the correct value shall be
returned. 
.SH ERRORS
.LP
These functions shall fail if:
.TP 7
Range\ Error
The result overflows. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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.
.sp
.LP
These functions may fail if:
.TP 7
Range\ Error
The result underflows. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
For IEEE\ Std\ 754-1985 \fBdouble\fP, 1024 <= \fIx\fP implies \fIexp2\fP(
\fIx\fP) has overflowed. The value
\fIx\fP <\ -1022 implies \fIexp\fP( \fIx\fP) has underflowed.
.LP
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.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIexp\fP(), \fIfeclearexcept\fP(), \fIfetestexcept\fP(), \fIisnan\fP(),
\fIlog\fP(), the
Base Definitions volume of IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment
of Error Conditions for Mathematical Functions, \fI<math.h>\fP
.SH 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 .