|LOG1P(3)||Linux Programmer's Manual||LOG1P(3)|
NAME¶log1p, log1pf, log1pl - logarithm of 1 plus argument
#include <math.h> double log1p(double x);Link with -lm.float log1pf(float x);long double log1pl(long double x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;or cc -std=c99
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;or cc -std=c99
DESCRIPTION¶log1p(x) returns a value equivalent to
log (1 + x)It 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
- An invalid floating-point exception (FE_INVALID) is raised.
- Pole error: x is -1
- A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.
Multithreading (see pthreads(7))¶The log1p(), log1pf(), and log1pl() functions are thread-safe.
CONFORMING TO¶C99, POSIX.1-2001.
SEE ALSO¶exp(3), expm1(3), log(3)
COLOPHON¶This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.