Seed based random generator

generated_world/src/main/java/mc/world/generated_world/SeedRandomGenerator.java

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+package mc.world.generated_world;
+
+public final class SeedRandomGenerator {
+
+    public static double random (int x, int y, int seed) {
+        x = Math.abs(x - y) + 1;
+        y = Math.abs(y - x) + 1;
+        for (int i = 0; i < 40; i ++) {
+            int a1 = x % 13;
+            int a2 = x % 31;
+            int a3 = x % 89;
+            int a4 = y % 359;
+            int a5 = y % 7;
+            int a6 = y % 313;
+            int a7 = y % 8461;
+            int a8 = y % 105467;
+            int a9 = x % 105943;
+            y = x + seed;
+            x += a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9;
+        }
+        return ((x + y) % 100000) / 100000d;
+    }
+}

generated_world/src/test/java/mc/world/generated_world/SeedRandomGeneratorTest.java

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+package mc.world.generated_world;
+
+import org.junit.Test;
+
+import javax.imageio.ImageIO;
+import java.awt.image.BufferedImage;
+import java.io.File;
+
+import static org.junit.Assert.*;
+
+public class SeedRandomGeneratorTest {
+    @Test
+    public void randomTest() throws Exception {
+        double maxDiff = 0;
+        double maxDisp = 0;
+        for (int i = 0; i < 100; i ++) {
+            double mid = 0;
+            double disp = 0;
+            int seed = (int) (Math.random() * Integer.MAX_VALUE);
+            for (int x = -1000; x < 1000; x++) {
+                for (int y = -1000; y < 1000; y++) {
+                    double rnd = SeedRandomGenerator.random(x, y, seed);
+                    mid += rnd;
+                    disp += (rnd - 0.5) * (rnd - 0.5);
+                }
+            }
+            mid = mid/4000000;
+            disp = Math.sqrt(disp)/4000000;
+            if (maxDiff < Math.abs(mid - 0.5)) {
+                maxDiff = Math.abs(mid - 0.5);
+            }
+            if (maxDisp < disp) {
+                maxDisp = disp;
+            }
+            System.out.printf("Iteration %d.\t mid: %.3f, \tdisp %.6f\n", i + 1, mid, disp);
+        }
+        System.out.printf("Max diff: %.3f\n", maxDiff);
+        System.out.printf("Max disp: %.6f\n", maxDisp);
+
+        assertTrue(maxDiff > 0);
+    }
+
+    @Test
+    public void generateImage () throws Exception {
+        int h = 500;
+        int w = 500;
+        BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
+
+        int seed = (int) (Math.random() * Integer.MAX_VALUE) / 1024;
+        for (int x = 0; x < w; x ++) {
+            for (int y = 0; y < h; y ++) {
+                image.setRGB(x, y, (int) (0xffffff * SeedRandomGenerator.random(x, y, seed)));
+            }
+        }
+        ImageIO.write(image, "bmp", new File("out", "seed_random.png"));
+    }
+
+}