expm1 (3)
Leading comments
Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com> and Copyright 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpages@gmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting deriv...
NAME
expm1, expm1f, expm1l  exponential minus 1SYNOPSIS
#include <math.h> double expm1(double x);Link with lm.
float expm1f(float x);
long double expm1l(long double x);
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
These functions return a value equivalent toexp(x)  1The result 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).Interface  Attribute  Value 
expm1(), expm1f(), expm1l()  Thread safety  MTSafe 
CONFORMING TO
C99, POSIX.12001, POSIX.12008.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.