expm1(3)                   Library Functions Manual                   expm1(3)

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)

Linux man-pages 6.7               2023-10-31                          expm1(3)