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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 2002-07-27 by Walter Harms
+.\" (walter.harms@informatik.uni-oldenburg.de)
+.\"
+.TH atanh 3 2024-05-02 "Linux man-pages (unreleased)"
+.SH NAME
+atanh, atanhf, atanhl \- inverse hyperbolic tangent function
+.SH LIBRARY
+Math library
+.RI ( libm ", " \-lm )
+.SH SYNOPSIS
+.nf
+.B #include <math.h>
+.P
+.BI "double atanh(double " x );
+.BI "float atanhf(float " x );
+.BI "long double atanhl(long double " x );
+.P
+.fi
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR atanh ():
+.nf
+ _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
+ || _XOPEN_SOURCE >= 500
+.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
+ || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+ || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.fi
+.P
+.BR atanhf (),
+.BR atanhl ():
+.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 calculate the inverse hyperbolic tangent of
+.IR x ;
+that is the value whose hyperbolic tangent is
+.IR x .
+.SH RETURN VALUE
+On success, these functions return the inverse hyperbolic tangent of
+.IR x .
+.P
+If
+.I x
+is a NaN, a NaN is returned.
+.P
+If
+.I x
+is +0 (\-0), +0 (\-0) is returned.
+.P
+If
+.I x
+is +1 or \-1,
+a pole error occurs,
+and the functions return
+.BR HUGE_VAL ,
+.BR HUGE_VALF ,
+or
+.BR HUGE_VALL ,
+respectively, with the mathematically correct sign.
+.P
+If the absolute value of
+.I x
+is greater than 1,
+a domain error occurs,
+and a NaN is returned.
+.\"
+.\" POSIX.1-2001 documents an optional range error for subnormal x;
+.\" glibc 2.8 does not do this.
+.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 less than \-1 or greater than +1
+.I errno
+is set to
+.BR EDOM .
+An invalid floating-point exception
+.RB ( FE_INVALID )
+is raised.
+.TP
+Pole error: \fIx\fP is +1 or \-1
+.I errno
+is set to
+.B ERANGE
+(but see BUGS).
+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 atanh (),
+.BR atanhf (),
+.BR atanhl ()
+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.
+.SH BUGS
+In glibc 2.9 and earlier,
+.\" Bug: https://www.sourceware.org/bugzilla/show_bug.cgi?id=6759
+.\" This can be seen in sysdeps/ieee754/k_standard.c
+when a pole error occurs,
+.I errno
+is set to
+.B EDOM
+instead of the POSIX-mandated
+.BR ERANGE .
+Since glibc 2.10, glibc does the right thing.
+.SH SEE ALSO
+.BR acosh (3),
+.BR asinh (3),
+.BR catanh (3),
+.BR cosh (3),
+.BR sinh (3),
+.BR tanh (3)