EXP(3P) POSIX Programmer's Manual EXP(3P)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.
NAME
exp, expf, expl — exponential function
SYNOPSIS
#include <math.h>
double exp(double x);
float expf(float x);
long double expl(long double x);
DESCRIPTION
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-e 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 the exponen‐
tial value of x.
If the correct value would cause overflow, a range error shall occur
and exp(), expf(), and expl() 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 exp(), expf(), and expl() shall return 0.0,
or (if the IEC 60559 Floating-Point option is not supported) an imple‐
mentation-defined value no greater in magnitude than DBL_MIN, FLT_MIN,
and LDBL_MIN, respectively.
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
Computing the Density of the Standard Normal Distribution
This function shows an implementation for the density of the standard
normal distribution using exp(). This example uses the constant M_PI
which is part of the XSI option.
#include <math.h>
double
normal_density (double x)
{
return exp(−x*x/2) / sqrt (2*M_PI);
}
APPLICATION USAGE
Note that for IEEE Std 754‐1985 double, 709.8 < x implies exp(x) has
overflowed. The value x< −708.4 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 ALSOfeclearexcept(), fetestexcept(), isnan(), log()
The Base Definitions volume of POSIX.1‐2008, Section 4.19, 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, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 EXP(3P)
