PROLOG

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

NAME

       acosh, acoshf, acoshl — inverse hyperbolic cosine functions

SYNOPSIS

       #include <math.h>

       double acosh(double x);
       float acoshf(float x);
       long double acoshl(long double x);

DESCRIPTION

       The functionality described on this reference page is aligned with the ISO C standard. Any
       conflict between the requirements described here and the ISO C standard is  unintentional.
       This volume of POSIX.1‐2017 defers to the ISO C standard.

       These functions shall compute the inverse hyperbolic cosine of their argument x.

       An  application  wishing  to  check for error situations should set errno to zero and call
       feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno  is  non-
       zero  or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,
       an error has occurred.

RETURN VALUE

       Upon successful completion, these functions shall return the inverse hyperbolic cosine  of
       their argument.

       For  finite  values of x < 1, a domain error shall occur, and either a NaN (if supported),
       or an implementation-defined value shall be returned.

       If x is NaN, a NaN shall be returned.

       If x is +1, +0 shall be returned.

       If x is +Inf, +Inf shall be returned.

       If x is -Inf, a domain error shall occur, and a NaN shall be returned.

ERRORS

       These functions shall fail if:

       Domain Error
                   The x argument is finite and less than +1.0, or is -Inf.

                   If the integer expression (math_errhandling & MATH_ERRNO)  is  non-zero,  then
                   errno  shall  be set to [EDOM].  If the integer expression (math_errhandling &
                   MATH_ERREXCEPT) is non-zero, then the invalid floating-point  exception  shall
                   be raised.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

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

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       cosh(), feclearexcept(), fetestexcept()

       The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of  Error  Conditions
       for Mathematical Functions, <math.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
       the Institute of Electrical and Electronics Engineers, Inc and The  Open  Group.   In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or  formatting errors that appear in this page are most likely to have
       been introduced during the conversion of the source files to man page  format.  To  report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .