log1p(3) Library Functions Manual log1p(3) NAME log1p, log1pf, log1pl - logarithm of 1 plus argument LIBRARY Math library (libm, -lm) SYNOPSIS #include 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 log1pf(), log1pl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 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 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 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. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). +--------------------------------------------+---------------+---------+ |Interface | Attribute | Value | +--------------------------------------------+---------------+---------+ |log1p (), log1pf (), log1pl () | Thread safety | MT-Safe | +--------------------------------------------+---------------+---------+ STANDARDS C11, POSIX.1-2008. HISTORY C99, POSIX.1-2001. BUGS 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. SEE ALSO exp(3), expm1(3), log(3) Linux man-pages 6.9 2024-05-02 log1p(3)