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ACOSH 3M "Jul 12, 2006" "SunOS 5.11" "Mathematical Library Functions"
acosh, acoshf, acoshl - inverse hyperbolic cosine functions

c99 [ flag... ] file... -lm [ library... ]
#include <math.h>

double acosh(double x);

float acoshf(float x);

long double acoshl(long double x);

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


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

For finite values of x < 1, a domain error occurs and NaN is returned.

If x is NaN, NaN is returned.

If x is +1, +0 is returned.

If x is +Inf, +Inf is returned.

If x is -Inf, a domain error occurs and NaN is returned.

For exceptional cases, matherr(3M) tabulates the values to be returned by acosh() as specified by SVID3 and XPG3.


These functions will fail if:

Domain Error

The x argument is finite and less than 1.0, or is -Inf. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the invalid floating-point exception is raised. The acosh() function sets errno to EDOM if x is less than 1.0.


An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

An application can also set errno to 0 before calling acosh(). On return, if errno is non-zero, an error has occurred. The acoshf() and acoshl() functions do not set errno.


See attributes(5) for descriptions of the following attributes:

Interface Stability Standard
MT-Level MT-Safe

cosh(3M), feclearexcept(3M), fetestexcept(3M), math.h(3HEAD), matherr(3M), attributes(5), standards(5)