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**NAME**

log1p, log1pf, log1pl - logarithm of 1 plus argument

**SYNOPSIS**

#include<math.h>doublelog1p(doublex);floatlog1pf(floatx);longdoublelog1pl(longdoublex);Link with-lm. Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):log1p(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCElog1pf(),log1pl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

**DESCRIPTION**

These functions return a value equivalent to log (1 +x) The result is computed in a way that is accurate even if the value ofxis near zero.

**RETURN** **VALUE**

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.

**ERRORS**

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 -1errnois set toEDOM(but see BUGS). An invalid floating-point exception (FE_INVALID) is raised. Pole error:xis -1errnois set toERANGE(but see BUGS). A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

**ATTRIBUTES**

For an explanation of the terms used in this section, seeattributes(7). ┌────────────────────────────┬───────────────┬─────────┐ │Interface│Attribute│Value│ ├────────────────────────────┼───────────────┼─────────┤ │log1p(),log1pf(),log1pl() │ Thread safety │ MT-Safe │ └────────────────────────────┴───────────────┴─────────┘

**CONFORMING** **TO**

C99, POSIX.1-2001, POSIX.1-2008.

**BUGS**

Before version 2.22, the glibc implementation did not seterrnotoEDOMwhen a domain error occurred. Before version 2.22, the glibc implementation did not seterrnotoERANGEwhen a range error occurred.

**SEE** **ALSO**

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

**COLOPHON**

This page is part of release 4.15 of the Linuxman-pagesproject. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2017-09-15 LOG1P(3)