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log1p, log1pf, log1pl - logarithm of 1 plus argument

#include<math.h>doublelog1p(doublex);floatlog1pf(floatx);longdoublelog1pl(longdoublex);Link with-lm. Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):log1p(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; orcc-std=c99log1pf(),log1pl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; orcc-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 ofxis near zero.

On success, these functions return the natural logarithm of(1+x). Ifxis a NaN, a NaN is returned. Ifxis positive infinity, positive infinity is returned. Ifxis -1, a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively. Ifxis less than -1 (including negative infinity), a domain error occurs, and a NaN (not a number) is returned.

Seemath_error(7) for information on how to determine whether an error has occurred when calling these functions. The following errors can occur: Domain error:xis less than -1 An invalid floating-point exception (FE_INVALID) is raised. Pole error:xis -1 A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised. These functions do not seterrno.

C99, POSIX.1-2001.

exp(3),expm1(3),log(3)

This page is part of release 3.24 of the Linuxman-pagesproject. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2008-08-05 LOG1P(3)