log1p, log1pf, log1pl − logarithm of 1 plus argument
Math library (libm, −lm)
#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
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). |
C11, POSIX.1-2008.
C99, POSIX.1-2001.
Before glibc 2.22, the glibc implementation did not set errno to EDOM when a domain error occurred.
Before glibc 2.22, the glibc implementation did not set errno to ERANGE when a range error occurred.
exp(3), expm1(3), log(3)