
EXPM1(3) Linux Programmer's Manual EXPM1(3)
NAME
expm1, expm1f, expm1l  exponential minus 1
SYNOPSIS
#include <math.h>
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
Link with lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
expm1():
_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 500 
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
expm1f(), expm1l():
_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
DESCRIPTION
expm1(x) returns a value equivalent to
exp(x)  1
It is computed in a way that is accurate even if the value of x is near zeroa case where
exp(x)  1 would be inaccurate due to subtraction of two numbers that are nearly equal.
RETURN VALUE
On success, these functions return exp(x)  1.
If x is a NaN, a NaN is returned.
If x is +0 (0), +0 (0) is returned.
If x is positive infinity, positive infinity is returned.
If x is negative infinity, 1 is returned.
If the result overflows, a range error occurs, and the functions return HUGE_VAL,
HUGE_VALF, or HUGE_VALL, respectively.
ERRORS
See math_error(7) for information on how to determine whether an error has occurred when
calling these functions.
The following errors can occur:
Range error, overflow
errno is set to ERANGE (but see BUGS). An overflow floatingpoint exception
(FE_OVERFLOW) is raised.
CONFORMING TO
C99, POSIX.12001.
BUGS
For some large negative x values (where the function result approaches 1), expm1() raises
a bogus underflow floatingpoint exception.
For some large positive x values, expm1() raises a bogus invalid floatingpoint exception
in addition to the expected overflow exception, and returns a NaN instead of positive
infinity.
Before version 2.11, the glibc implementation did not set errno to ERANGE when a range
error occurred.
SEE ALSO
exp(3), log(3), log1p(3)
COLOPHON
This page is part of release 3.53 of the Linux manpages project. A description of the
project, and information about reporting bugs, can be found at
http://www.kernel.org/doc/manpages/.
20100912 EXPM1(3) 
