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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 ||
           _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 float-
       ing-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 3.53 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)