ACOSH(3) Library Functions Manual ACOSH(3)

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

[CX] 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.1-2024 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 [MX] either a NaN (if supported), or an implementation-defined value shall be returned.

[MX] 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, [MX] 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.