A piece of code, I want to know his inner workings

[shanfl]

There is a piece code in file 'sources/engine/Stride.Rendering/Rendering/Lights/LightClusteredPointSpotGroupRenderer.cs', I find it in many project ,like tiled forward rendering . but I reall hard to understand what it mean .

private static void UpdateClipRegion(
                        float lc,          // Light x/y coordinate (view space)
                        float lz,          // Light z coordinate (view space)
                        float lightRadius,
                        float cameraScale, // Project scale for coordinate (_11 or _22 for x/y respectively)
                        float cameraOffset, // Project offset for coordinate (_31 or _32 for x/y respectively)
                        ref float clipMin,
                        ref float clipMax)
            {
                float rSq = lightRadius * lightRadius;
                float lcSqPluslzSq = lc * lc + lz * lz;
                float d = rSq * lc * lc - lcSqPluslzSq * (rSq - lz * lz);

                '''
            }

In begin of this function , there is

                float rSq = lightRadius * lightRadius;
                float lcSqPluslzSq = lc * lc + lz * lz;
                float d = rSq * lc * lc - lcSqPluslzSq * (rSq - lz * lz);

I wonder about his rationale! plz.