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
_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).
|log1p(), log1pf(), log1pl()||Thread safety||MT-Safe|
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)
The man pages log1pf(3) and log1pl(3) are aliases of log1p(3).