Section (3) log
log, logf, logl — natural logarithmic function
||long double x
On success, these functions return the natural logarithm
x is a NaN, a
NaN is returned.
x is 1, the
result is +0.
x is positive
infinity, positive infinity is returned.
x is zero, then
a pole error occurs, and the functions return -
HUGE_VALF, or -
x is negative
(including negative infinity), then 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:
errnois set to EDOM. An invalid floating-point exception (
FE_INVALID) is raised.
- Pole error:
errnois set to ERANGE. A divide-by-zero floating-point exception (
FE_DIVBYZERO) is raised.
For an explanation of the terms used in this section, see attributes(7).
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
In glibc 2.5 and earlier, taking the
log() of a NaN produces a bogus invalid
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Linux libc source code
Lewine_zsingle_quotesz_s _POSIX Programmer_zsingle_quotesz_s Guide_ (O_zsingle_quotesz_Reilly & Associates, 1991)
386BSD man pages
Modified 1993-07-24 by Rik Faith (faithcs.unc.edu)
Modified 1995-08-14 by Arnt Gulbrandsen <agulbratroll.no>
Modified 2002-07-27 by Walter Harms