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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
   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 4.09 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/.

                              2016-03-15                          EXPM1(3)



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