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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,
       respectively.

ERRORS
       See  math_error(7)  for  information on how to determine whether an error has occurred when calling these func-
       tions.

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



                                  2008-08-05                          EXPM1(3)