EXPM1(3)Linux Programmer's ManualEXPM1(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 (seefeature_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 zero--a case where exp(x) - 1 would be inaccurate due to sub- traction 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 Seemath_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 floating- point exception (FE_OVERFLOW) is raised. ATTRIBUTES For an explanation of the terms used in this section, seeattributes(7). +----------------------------+---------------+---------+ |Interface | Attribute | Value | +----------------------------+---------------+---------+ |expm1(), expm1f(), expm1l() | Thread safety | MT-Safe | +----------------------------+---------------+---------+ CONFORMING TO C99, POSIX.1-2001, POSIX.1-2008. BUGS For some large negative x values (where the function result approaches -1), expm1() raises a bogus underflow floating-point exception. For some large positive x values, expm1() raises a bogus invalid float- ing-point 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 ALSOexp(3),log(3),log1p(3)COLOPHON This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2017-09-15EXPM1(3)