Cg 3.1 Toolkit Documentation Cg / Standard Library / acos

## Name

acos - returns arccosine of scalars and vectors.

## Synopsis

```float  acos(float a);
float1 acos(float1 a);
float2 acos(float2 a);
float3 acos(float3 a);
float4 acos(float4 a);

half   acos(half a);
half1  acos(half1 a);
half2  acos(half2 a);
half3  acos(half3 a);
half4  acos(half4 a);

fixed  acos(fixed a);
fixed1 acos(fixed1 a);
fixed2 acos(fixed2 a);
fixed3 acos(fixed3 a);
fixed4 acos(fixed4 a);
```

## Parameters

a
Vector or scalar of which to determine the arccosine.

## Description

Returns the arccosine of a in the range [0,pi], expecting a to be in the range [-1,+1].

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

## Reference Implementation

acos for a float scalar could be implemented like this.

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

// Absolute error <= 6.7e-5
float acos(float x) {
float negate = float(x < 0);
x = abs(x);
float ret = -0.0187293;
ret = ret * x;
ret = ret + 0.0742610;
ret = ret * x;
ret = ret - 0.2121144;
ret = ret * x;
ret = ret + 1.5707288;
ret = ret * sqrt(1.0-x);
ret = ret - 2 * negate * ret;
return negate * 3.14159265358979 + ret;
}
```

## Profile Support

acos is supported in all profiles.

Support in the fp20 is limited.