expm1, expm1f, expm1l - exponential minus 1
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)):
expm1():
_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:
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).
Interface | Attribute | Value |
Thread safety | MT-Safe |
C11, POSIX.1-2008.
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.