log1p3
Logarithm of 1 plus argument
Usage
#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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
log1pf(), log1pl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Library
Math library (libm, -lm)
Overview
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.
-
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
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| log1p(), log1pf(), log1pl() | Thread safety | MT-Safe |
Releases
19 releases since Debian 1.1 (Buzz); the text changed 13 times.