LOG1P(3) Linux Programmer's Manual LOG1P(3)
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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99 log1pf(), log1pl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99
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.
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 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. These functions do not set errno.
exp(3), expm1(3), log(3)
This page is part of release 3.61 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2010-09-20 LOG1P(3)
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