##### Synopsis

    #include <math.h>
    float acoshf(float x);

##### Description

acoshf returns the non-negative inverse hyperbolic cosine of x.

##### Fast math library behavior

If x< 1, errno is set to EDOM and acoshf returns HUGE_VALF.

##### IEC 60559 math library behavior

If x < 1, acoshf returns NaN with signal.
If x is NaN, acoshf returns NaN without signal.

##### Portability

acoshf conforms to ISO/IEC 9899:1999 (C99).