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+'\" t
+.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
+.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
+.\"     <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" References consulted:
+.\"     Linux libc source code
+.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
+.\"     386BSD man pages
+.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
+.\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no>
+.\" Modified 2002-07-27 by Walter Harms
+.\" 	(walter.harms@informatik.uni-oldenburg.de)
+.\"
+.TH log 3 (date) "Linux man-pages (unreleased)"
+.SH NAME
+log, logf, logl \- natural logarithmic function
+.SH LIBRARY
+Math library
+.RI ( libm ", " \-lm )
+.SH SYNOPSIS
+.nf
+.B #include <math.h>
+.P
+.BI "double log(double " x );
+.BI "float logf(float " x );
+.BI "long double logl(long double " x );
+.fi
+.P
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR logf (),
+.BR logl ():
+.nf
+    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
+        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.fi
+.SH DESCRIPTION
+These functions return the natural logarithm of
+.IR x .
+.SH RETURN VALUE
+On success, these functions return the natural logarithm of
+.IR x .
+.P
+If
+.I x
+is a NaN,
+a NaN is returned.
+.P
+If
+.I x
+is 1, the result is +0.
+.P
+If
+.I x
+is positive infinity,
+positive infinity is returned.
+.P
+If
+.I x
+is zero,
+then a pole error occurs, and the functions return
+.RB \- HUGE_VAL ,
+.RB \- HUGE_VALF ,
+or
+.RB \- HUGE_VALL ,
+respectively.
+.P
+If
+.I x
+is negative (including negative infinity), then
+a domain error occurs, and a NaN (not a number) is returned.
+.SH ERRORS
+See
+.BR math_error (7)
+for information on how to determine whether an error has occurred
+when calling these functions.
+.P
+The following errors can occur:
+.TP
+Domain error: \fIx\fP is negative
+.I errno
+is set to
+.BR EDOM .
+An invalid floating-point exception
+.RB ( FE_INVALID )
+is raised.
+.TP
+Pole error: \fIx\fP is zero
+.I errno
+is set to
+.BR ERANGE .
+A divide-by-zero floating-point exception
+.RB ( FE_DIVBYZERO )
+is raised.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR log (),
+.BR logf (),
+.BR logl ()
+T}	Thread safety	MT-Safe
+.TE
+.SH STANDARDS
+C11, POSIX.1-2008.
+.SH HISTORY
+C99, POSIX.1-2001.
+.P
+The variant returning
+.I double
+also conforms to
+SVr4, 4.3BSD, C89.
+.SH BUGS
+In glibc 2.5 and earlier,
+taking the
+.BR log ()
+of a NaN produces a bogus invalid floating-point
+.RB ( FE_INVALID )
+exception.
+.SH SEE ALSO
+.BR cbrt (3),
+.BR clog (3),
+.BR log10 (3),
+.BR log1p (3),
+.BR log2 (3),
+.BR sqrt (3)