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

       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 4.04 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 http://www.kernel.org/doc/man-pages/.

                                            2015-04-19                                   EXPM1(3)