expm1, expm1f, expm1l - exponential minus 1
#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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 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.
x is a NaN, a NaN is returned.
x is +0 (-0), +0 (-0) is returned.
x is positive infinity, positive infinity is
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:
errno is set to ERANGE (but see BUGS). An
overflow floating-point exception (FE_OVERFLOW) is
C99, POSIX.1-2001, POSIX.1-2008.
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 version 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
Before version 2.11, the glibc implementation did not set
errno to ERANGE when a range error
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