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Name

expm1, expm1f, expm1l - exponential minus 1

Synopsis


#include <math.h>
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) ):

expm1():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

expm1f(), expm1l():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

Description

expm1(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.

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

Multithreading (see pthreads(7) )

The expm1(), expm1f(), and expm1l() functions are thread-safe.

Conforming to

C99, POSIX.1-2001.

Bugs

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 floating-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 Also

exp(3) , log(3) , log1p(3)

Colophon

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