quaternion to 3x3

q23x3.cs

using Unity.Mathematics;

public static class QuaternionTo3x3 {
    public static float3x3 To3x3(this quaternion quat) {
        float4 q = quat.value;

        float4x4 leftConversionMatrix = new float4x4(
            new float4(q.w, q.z, -q.y, q.x),
            new float4(-q.z, q.w, q.x, q.y),
            new float4(q.y, -q.x, q.w, q.z),
            new float4(-q.x, -q.y, -q.z, q.w)
        );

        float4x4 rightConversionMatrix = new float4x4(
            new float4(q.w, q.z, -q.y, -q.x),
            new float4(-q.z, q.w, q.x, -q.y),
            new float4(q.y, -q.x, q.w, -q.z),
            new float4(q.x, q.y, q.z, q.w)
        );

        float4x4 rot = math.mul(leftConversionMatrix, rightConversionMatrix);

        return new float3x3(
            new float3(rot.c0.x, rot.c0.y, rot.c0.z),
            new float3(rot.c1.x, rot.c1.y, rot.c1.z),
            new float3(rot.c2.x, rot.c2.y, rot.c2.z)
        );
    }
}