> ## Name

> asin - returns arcsine of scalars and vectors.

> ## Synopsis

>     float  asin(float a);
>     float1 asin(float1 a);
>     float2 asin(float2 a);
>     float3 asin(float3 a);
>     float4 asin(float4 a);

>     half   asin(half a);
>     half1  asin(half1 a);
>     half2  asin(half2 a);
>     half3  asin(half3 a);
>     half4  asin(half4 a);

>     fixed  asin(fixed a);
>     fixed1 asin(fixed1 a);
>     fixed2 asin(fixed2 a);
>     fixed3 asin(fixed3 a);
>     fixed4 asin(fixed4 a);

> ## Parameters

> a
>   Vector or scalar of which to determine the arcsine.

> ## Description

> Returns the arcsine of a in the range [-pi/2,+pi/2], expecting a to be in the range [-1,+1].

> For vectors, the returned vector contains the arcsine of each element of the input vector.

> ## Reference Implementation

> asin for a float scalar could be implemented like this.

>     // Handbook of Mathematical Functions
>     // M. Abramowitz and I.A. Stegun, Ed.

>     float asin(float x) {
>       float negate = float(x < 0);
>       x = abs(x);
>       float ret = -0.0187293;
>       ret *= x;
>       ret += 0.0742610;
>       ret *= x;
>       ret -= 0.2121144;
>       ret *= x;
>       ret += 1.5707288;
>       ret = 3.14159265358979*0.5 - sqrt(1.0 - x)*ret;
>       return ret - 2 * negate * ret;
>     }

> ## Profile Support

> asin is supported in all profiles.

> Support in the fp20 is limited.

> ## See Also

> abs, acos, sin, sqrt