expm1 (3)  Linux Manuals
expm1: exponential minus 1
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():

_ISOC99_SOURCE  _POSIX_C_SOURCE >= 200112L
 _XOPEN_SOURCE >= 500
 /* Since glibc 2.19: */ _DEFAULT_SOURCE
 /* Glibc versions <= 2.19: */ _BSD_SOURCE  _SVID_SOURCE
expm1f(), expm1l():

_ISOC99_SOURCE  _POSIX_C_SOURCE >= 200112L
 /* Since glibc 2.19: */ _DEFAULT_SOURCE
 /* Glibc versions <= 2.19: */ _BSD_SOURCE  _SVID_SOURCE
DESCRIPTION
These functions return a value equivalent to
exp(x)  1
The 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
Before glibc 2.17, on certain architectures (e.g., x86, but not x86_64) expm1() raised a bogus underflow floatingpoint exception for some large negative x values (where the function result approaches 1),Before approximately glibc version 2.11, expm1() raised a bogus invalid floatingpoint exception in addition to the expected overflow exception, and returned a NaN instead of positive infinity. for some large positive x values,
Before version 2.11, the glibc implementation did not set errno to ERANGE when a range error occurred.
COLOPHON
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