3. Library calls (functions within program libraries)
EXPM1
Section: Linux Programmer's Manual (3)Updated: 20170915
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NAME
expm1, expm1f, expm1l  exponential minus 1SYNOPSIS
#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
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
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