## Linux and UNIX Man Pages

Test Your Knowledge in Computers #487
Difficulty: Easy
A program's entry point is always defined by a main function or method.
True or False?

# expm1(3) [redhat man page]

```EXPM1(3)						     Linux Programmer's Manual							  EXPM1(3)

NAME
expm1, log1p - exponential minus 1, logarithm of 1 plus argument

SYNOPSIS
#include <math.h>

double expm1(double x);

double log1p(double x);

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.

log1p(x) returns a value equivalent to `log (1 + x)'. It is computed in a way that is accurate even if the value of x is near zero.

CONFORMING TO
BSD

exp(3), log(3)

GNU								    1995-09-16								  EXPM1(3)```

## Check Out this Related Man Page

```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);

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  subtrac-
tion 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 floating-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.