LOG1P(3) Linux Programmer's Manual 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 oc-
curs, 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
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 float-
ing-point exception (FE_DIVBYZERO) is raised.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
+----------------------------+---------------+---------+
|Interface | Attribute | Value |
+----------------------------+---------------+---------+
|log1p(), log1pf(), log1pl() | Thread safety | MT-Safe |
+----------------------------+---------------+---------+
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
BUGS
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.
SEE ALSO
exp(3), expm1(3), log(3)
COLOPHON
This page is part of release 5.07 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/.
2017-09-15 LOG1P(3)