### 2.5 `casin`, `casinf`—complex arc sine

Synopsis

    #include <complex.h>
    double complex casin(double complex z);
    float complex casinf(float complex z);

Description
These functions compute the complex arc sine of z, with branch cuts outside the interval [-1, +1] along the real axis.

`casinf` is identical to `casin`, except that it performs its calculations on `floats complex`.

Returns
These functions return the complex arc sine value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [-pi/2, +pi/2] along the real axis.

Portability
`casin` and `casinf` are ISO C99