Optimize and clean up LineIrradiance()

Assets/ScriptableRenderLoop/ShaderLibrary/AreaLighting.hlsl

     return PolygonRadiance(L, twoSided);
 }
 
-float LineFpo(float l, float rcpD, float rcpDL)
+float LineFpo(float tLDDL, float lrcpD, float rcpD)
-    // Compute: l / d / (d * d + l * l) + 1.0 / (d * d) * atan(l / d).
-    return l * rcpDL + sq(rcpD) * atan(l * rcpD);
+    // Compute: ((l / d) / (d * d + l * l)) + (1.0 / (d * d)) * atan(l / d).
+    return tLDDL + sq(rcpD) * atan(lrcpD);
-float LineFwt(float sqL, float rcpDL)
+float LineFwt(float tLDDL, float l)
-    // Compute: l * l / d / (d * d + l * l).
-    return sqL * rcpDL;
+    // Compute: l * ((l / d) / (d * d + l * l)).
+    return l * tLDDL;
 }
 
 // Computes the integral of the clamped cosine over the line segment.
 // the shaded point and the line, pointing away from the shaded point.
 float LineIrradiance(float l1, float l2, float3 normal, float3 tangent)
 {   
-    float dist   = length(normal);
-    float rcpDL1 = rcp(dist) * rcp(sq(dist) + sq(l1));
-    float rcpDL2 = rcp(dist) * rcp(sq(dist) + sq(l2));
-    float intP0  = LineFpo(l2, rcp(dist), rcpDL2) - LineFpo(l1, rcp(dist), rcpDL1);
-    float intWt  = LineFwt(sq(l2), rcpDL2) - LineFwt(sq(l1), rcpDL1);
+    float d      = length(normal);
+    float l1rcpD = l1 * rcp(d);
+    float l2rcpD = l2 * rcp(d);
+    float tLDDL1 = l1rcpD * rcp(sq(d) + sq(l1));
+    float tLDDL2 = l2rcpD * rcp(sq(d) + sq(l2));
+    float intWt  = LineFwt(tLDDL2, l2) - LineFwt(tLDDL1, l1);
+    float intP0  = LineFpo(tLDDL2, l2rcpD, rcp(d)) - LineFpo(tLDDL1, l1rcpD, rcp(d));
     return intP0 * normal.z + intWt * tangent.z;
 }