1ATANH(3P)                  POSIX Programmer's Manual                 ATANH(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
10

NAME

12       atanh, atanhf, atanhl — inverse hyperbolic tangent functions
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SYNOPSIS

15       #include <math.h>
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17       double atanh(double x);
18       float atanhf(float x);
19       long double atanhl(long double x);
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DESCRIPTION

22       The functionality described on this reference page is aligned with  the
23       ISO C  standard.  Any  conflict between the requirements described here
24       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2017
25       defers to the ISO C standard.
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27       These  functions  shall compute the inverse hyperbolic tangent of their
28       argument x.
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30       An application wishing to check for error situations should  set  errno
31       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
32       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
33       FE_DIVBYZERO  |  FE_OVERFLOW  | FE_UNDERFLOW) is non-zero, an error has
34       occurred.
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RETURN VALUE

37       Upon successful completion, these functions shall  return  the  inverse
38       hyperbolic tangent of their argument.
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40       If  x  is  ±1,  a  pole  error  shall occur, and atanh(), atanhf(), and
41       atanhl() shall return the value of the macro HUGE_VAL,  HUGE_VALF,  and
42       HUGE_VALL, respectively, with the same sign as the correct value of the
43       function.
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45       For finite |x|>1, a domain error shall occur, and either a NaN (if sup‐
46       ported), or an implementation-defined value shall be returned.
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48       If x is NaN, a NaN shall be returned.
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50       If x is ±0, x shall be returned.
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52       If x is ±Inf, a domain error shall occur, and a NaN shall be returned.
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54       If x is subnormal, a range error may occur
55       and x should be returned.
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57       If  x  is not returned, atanh(), atanhf(), and atanhl() shall return an
58       implementation-defined value no  greater  in  magnitude  than  DBL_MIN,
59       FLT_MIN, and LDBL_MIN, respectively.
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ERRORS

62       These functions shall fail if:
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64       Domain Error
65                   The x argument is finite and not in the range [-1,1], or is
66                   ±Inf.
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68                   If the integer expression (math_errhandling  &  MATH_ERRNO)
69                   is  non-zero,  then  errno  shall be set to [EDOM].  If the
70                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
71                   non-zero,  then  the invalid floating-point exception shall
72                   be raised.
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74       Pole Error  The x argument is ±1.
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76                   If the integer expression (math_errhandling  &  MATH_ERRNO)
77                   is  non-zero,  then errno shall be set to [ERANGE].  If the
78                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
79                   non-zero,  then the divide-by-zero floating-point exception
80                   shall be raised.
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82       These functions may fail if:
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84       Range Error The value of x is subnormal.
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86                   If the integer expression (math_errhandling  &  MATH_ERRNO)
87                   is  non-zero,  then errno shall be set to [ERANGE].  If the
88                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
89                   non-zero, then the underflow floating-point exception shall
90                   be raised.
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92       The following sections are informative.
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EXAMPLES

95       None.
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APPLICATION USAGE

98       On  error,  the  expressions  (math_errhandling   &   MATH_ERRNO)   and
99       (math_errhandling  & MATH_ERREXCEPT) are independent of each other, but
100       at least one of them must be non-zero.
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RATIONALE

103       None.
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FUTURE DIRECTIONS

106       None.
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SEE ALSO

109       feclearexcept(), fetestexcept(), tanh()
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111       The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of
112       Error Conditions for Mathematical Functions, <math.h>
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115       Portions  of  this text are reprinted and reproduced in electronic form
116       from IEEE Std 1003.1-2017, Standard for Information Technology --  Por‐
117       table  Operating System Interface (POSIX), The Open Group Base Specifi‐
118       cations Issue 7, 2018 Edition, Copyright (C) 2018 by the  Institute  of
119       Electrical  and  Electronics Engineers, Inc and The Open Group.  In the
120       event of any discrepancy between this version and the original IEEE and
121       The  Open Group Standard, the original IEEE and The Open Group Standard
122       is the referee document. The original Standard can be  obtained  online
123       at http://www.opengroup.org/unix/online.html .
124
125       Any  typographical  or  formatting  errors that appear in this page are
126       most likely to have been introduced during the conversion of the source
127       files  to  man page format. To report such errors, see https://www.ker‐
128       nel.org/doc/man-pages/reporting_bugs.html .
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132IEEE/The Open Group                  2017                            ATANH(3P)
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