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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or cc -std=c99
       expm1f(), expm1l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; 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,  respec-
       tively.

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
              An overflow floating-point exception (FE_OVERFLOW) is raised.

       These functions do not set errno.

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.

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

COLOPHON
       This  page  is  part of release 3.25 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/.



                                                           2008-08-05                                                   EXPM1(3)