add minor improvements to perlin noise performance

src/main/java/eu/jonahbauer/raytracing/render/texture/PerlinTexture.java

@@ -91,11 +91,11 @@ public final class PerlinTexture implements Texture {
         int j = (int) Math.floor(y);
         int k = (int) Math.floor(z);
 
-        var c = new Vec3[2][2][2];
+        var c = new Vec3[8];
         for (int di = 0; di < 2; di++) {
             for (int dj = 0; dj < 2; dj++) {
                 for (int dk = 0; dk < 2; dk++) {
-                    c[di][dj][dk] = randvec[permX[(i + di) & mask] ^ permY[(j + dj) & mask] ^ permZ[(k + dk) & mask]];
+                    c[di << 2 | dj << 1 | dk] = randvec[permX[(i + di) & mask] ^ permY[(j + dj) & mask] ^ permZ[(k + dk) & mask]];
                 }
             }
         }
@@ -109,7 +109,7 @@ public final class PerlinTexture implements Texture {
         var weight = 1.0;
 
         for (int i = 0; i < depth; i++) {
-            accum += weight * getNoise(temp);
+            accum = Math.fma(weight, getNoise(temp), accum);
             weight *= 0.5;
             temp = temp.times(2);
         }
@@ -124,20 +124,21 @@ public final class PerlinTexture implements Texture {
         return color.apply(t);
     }
 
-    private static double interpolate(Vec3[][][] c, double u, double v, double w) {
-        var uu = u * u * (3 - 2 * u);
-        var vv = v * v * (3 - 2 * v);
-        var ww = w * w * (3 - 2 * w);
+    private static double interpolate(Vec3[] c, double u, double v, double w) {
+        var uu = u * u * Math.fma(-2, u, 3);
+        var vv = v * v * Math.fma(-2, v, 3);
+        var ww = w * w * Math.fma(-2, w, 3);
 
         var accum = 0.0;
         for (int i = 0; i < 2; i++) {
             for (int j = 0; j < 2; j++) {
                 for (int k = 0; k < 2; k++) {
-                    var weight = new Vec3(u - i, v - j, w - k);
-                    accum += (i * uu + (1 - i) * (1 - uu))
-                             * (j * vv + (1 - j) * (1 - vv))
-                             * (k * ww + (1 - k) * (1 - ww))
-                             * c[i][j][k].times(weight);
+                    var vec = c[i << 2 | j << 1 | k];
+                    var dot = (u - i) * vec.x() + (v - j) * vec.y() + (w - k) * vec.z();
+                    accum += Math.fma(i, uu, (1 - i) * (1 - uu))
+                             * Math.fma(j, vv, (1 - j) * (1 - vv))
+                             * Math.fma(k, ww, (1 - k) * (1 - ww))
+                             * dot;
                 }
             }
         }