log1p, log1pf, log1pl - logarithm of 1 plus argument
#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
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.
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.
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.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| log1p (), log1pf (), log1pl () |
Thread safety |
MT-Safe |
C99, POSIX.1-2001, POSIX.1-2008.
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)