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.1‐2008 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.1‐2008, Section 4.19, 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, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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 .