expm1(3) Library Functions Manual expm1(3) NAME expm1, expm1f, expm1l - exponential minus 1 LIBRARY Math library (libm, -lm) SYNOPSIS #include double expm1(double x); float expm1f(float x); long double expm1l(long double x); 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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE expm1f(), expm1l(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 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 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 floating- point 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 | MT-Safe | +--------------------------------------------+---------------+---------+ STANDARDS C11, POSIX.1-2008. HISTORY C99, POSIX.1-2001. BSD. BUGS Before glibc 2.17, on certain architectures (e.g., x86, but not x86_64) expm1() raised a bogus underflow floating-point exception for some large negative x values (where the function result approaches -1). Before approximately glibc 2.11, expm1() raised a bogus invalid floating-point exception in addition to the expected overflow exception, and returned a NaN instead of positive infinity, for some large positive x values. Before glibc 2.11, the glibc implementation did not set errno to ERANGE when a range error occurred. SEE ALSO exp(3), log(3), log1p(3) Linux man-pages 6.8 2024-05-02 expm1(3)