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

       expm1(x) returns a value equivalent to

           exp(x) - 1

       It 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.

CONFORMING TO

       C99, POSIX.1-2001.

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 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

                                                   2010-09-12                                           EXPM1(3)