```LOG1P(3)                  Linux Programmer's Manual                 LOG1P(3)
```

## NAME         top

```       log1p, log1pf, log1pl -  logarithm of 1 plus argument
```

## SYNOPSIS         top

```       #include <math.h>

double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

log1p():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
log1pf(), log1pl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION         top

```       These functions return a value equivalent to

log (1 + x)

The result is computed in a way that is accurate even if the value of
x is near zero.
```

## RETURN VALUE         top

```       On success, these functions return the natural logarithm of (1 + x).

If x is a NaN, a NaN is returned.

If x is positive infinity, positive infinity is returned.

If x is -1, a pole error occurs, and the functions return -HUGE_VAL,
-HUGE_VALF, or -HUGE_VALL, respectively.

If x is less than -1 (including negative infinity), a domain error
occurs, and a NaN (not a number) is returned.
```

## ERRORS         top

```       See math_error(7) for information on how to determine whether an
error has occurred when calling these functions.

The following errors can occur:

Domain error: x is less than -1
errno is set to EDOM (but see BUGS).  An invalid floating-
point exception (FE_INVALID) is raised.

Pole error: x is -1
errno is set to ERANGE (but see BUGS).  A divide-by-zero
floating-point exception (FE_DIVBYZERO) is raised.
```

## ATTRIBUTES         top

```       For an explanation of the terms used in this section, see
attributes(7).

┌────────────────────────────┬───────────────┬─────────┐
│Interface                   │ Attribute     │ Value   │
├────────────────────────────┼───────────────┼─────────┤
│log1p(), log1pf(), log1pl() │ Thread safety │ MT-Safe │
└────────────────────────────┴───────────────┴─────────┘
```

## CONFORMING TO         top

```       C99, POSIX.1-2001, POSIX.1-2008.
```

## BUGS         top

```       Before version 2.22, the glibc implementation did not set errno to
EDOM when a domain error occurred.

Before version 2.22, the glibc implementation did not set errno to
ERANGE when a range error occurred.
```

```       exp(3), expm1(3), log(3)
```

## COLOPHON         top

```       This page is part of release 5.00 of the Linux man-pages project.  A
description of the project, information about reporting bugs, and the