Math library (libm, -lm)
#include <math.h> 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)):
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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.
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.
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.
For an explanation of the terms used in this section, see attributes(7).
|expm1(), expm1f(), expm1l()||Thread safety||MT-Safe|
C99, POSIX.1-2001. BSD.
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.
exp(3), log(3), log1p(3)
The man pages expm1f(3) and expm1l(3) are aliases of expm1(3).