NAME

       expm1, expm1f, expm1l - exponential minus 1

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       double expm1(double x);
       float expm1f(float x);
       long double expm1l(long double x);

   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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       expm1f(), expm1l():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C99, POSIX.1-2001.  BSD.

BUGS

       Before glibc 2.17, on certain architectures (e.g., x86, but not x86_64) expm1()  raised  a
       bogus  underflow  floating-point  exception  for  some  large negative x values (where the
       function result approaches -1).

       Before approximately glibc 2.11, expm1() raised a bogus invalid  floating-point  exception
       in  addition  to  the  expected overflow exception, and returned a NaN instead of positive
       infinity, for some large positive x values.

       Before glibc 2.11, the glibc implementation did not set errno to ERANGE when a range error
       occurred.

SEE ALSO

       exp(3), log(3), log1p(3)