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)