expm1(3) — Linux manual page


EXPM1(3)                Linux Programmer's Manual               EXPM1(3)

NAME         top

       expm1, expm1f, expm1l - exponential minus 1

SYNOPSIS         top

       #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

           _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         top

       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

RETURN VALUE         top

       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         top

       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         top

       For an explanation of the terms used in this section, see

       │Interface                             Attribute     Value   │
       │expm1(), expm1f(), expm1l()           │ Thread safety │ MT-Safe │

CONFORMING TO         top

       C99, POSIX.1-2001, POSIX.1-2008.

BUGS         top

       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 x values.

       Before version 2.11, the glibc implementation did not set errno
       to ERANGE when a range error occurred.

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

                               2021-03-22                       EXPM1(3)

Pages that refer to this page: exp(3)log1p(3)