LOG1P(3)

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

SYNOPSIS
#include <math.h>

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

Link with -lm.

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
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
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
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
    An invalid floating-point exception (FE_INVALID) is raised.

Pole error: x is -1
    A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

These functions do not set errno.

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value
 | Thread safety | MT-Safe

CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.

SEE ALSO
exp(3), expm1(3), log(3)

COLOPHON
This page is part of release 4.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.