expm1

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

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():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
       expm1f(), expm1l():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 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  sub-
       traction 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  at-
       tributes(7).

       +----------------------------+---------------+---------+
       |Interface                   | Attribute     | Value   |
       +----------------------------+---------------+---------+
       |expm1(), expm1f(), expm1l() | Thread safety | MT-Safe |
       +----------------------------+---------------+---------+
CONFORMING TO
       C99, POSIX.1-2001, POSIX.1-2008.

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

COLOPHON
       This  page  is  part of release 5.05 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
       https://www.kernel.org/doc/man-pages/.

                                  2017-09-15                          EXPM1(3)