expm1(3) Linux Man Page - System Grab Bag

Name

expm1, expm1f, expm1l - exponential minus 1

Library

Math library ( libm ", " -lm )

Synopsis

#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

expm1f() expm1l()

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

Description

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.

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

For an explanation of the terms used in this section, see attributes(7). allbox; lbx lb lb T{ expm1()expm1f()expm1l()

Interface	Attribute	Value
T}	Thread safety	MT-Safe

Standards

C11, POSIX.1-2008.

History

C99, POSIX.1-2001. BSD.

Bugs

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.