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  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).

       ┌────────────────────────────┬───────────────┬─────────┐
       │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 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

       This page is part of release 4.15 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)