The asin() function computes the principal value of the arc sine of x. The value of x should be in the range [-1,1].

Upon successful completion, asin() returns the arc sine of x, in the range [-pi/2,pi/2] radians. If the value of x is not in the range [-1,1] and is not +-Inf or NaN, either 0.0 or NaN is returned and errno is set to EDOM.

If x is NaN, NaN is returned.

If x is +-Inf, either 0.0 is returned and errno is set to EDOM or NaN is returned and errno may be set to EDOM.

For exceptional cases, matherr(3M) tabulates the values to be returned as dictated by Standards other than XPG4.

The asin() function will fail if:

EDOM

The value x is not +-Inf or NaN and is not in the range [-1,1].

The asin() function may fail if:

EDOM

The value of x is +-Inf.

An application wishing to check for error situations should set errno to 0, then call asin(). If errno is non-zero on return, or the return value is NaN, an error has occurred.

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

isnan(3M), matherr(3M), sin(3M), attributes(5), standards(5)