EXPM1(3) Linux Programmer's Manual EXPM1(3)NAME
expm1, expm1f, expm1l - exponential minus 1
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTIONexpm1(x) returns a value equivalent to
exp(x) - 1
It 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.
Multithreading (see pthreads(7))
The expm1(), expm1f(), and expm1l() functions are thread-safe.
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
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