Unsynchronized deposit clump random

- Draw deposit clump randomness from a single-owner generator with the java.util.Random sequence

core/src/main/java/art/arcane/iris/generation/stage/IrisDepositModifier.java

@@ -227,7 +227,7 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
         int engineHeight = getEngine().getHeight();
         List<PreparedClump> clumps = new ArrayList<>(limit - first);
         for (int l = first; l < limit; l++) {
-            RNG clumpRng = new RNG(clumpSeed(plan.seed(), l));
+            RNG clumpRng = new ClumpRandom(clumpSeed(plan.seed(), l));
             if (k.getPerClumpSpawnChance() < clumpRng.d()) {
                 continue;
             }
@@ -635,6 +635,30 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
     private record PackScan(IrisData data, boolean variants, boolean oreScaling) {
     }
 
+    static final class ClumpRandom extends RNG {
+        private static final long MULTIPLIER = 0x5DEECE66DL;
+        private static final long ADDEND = 0xBL;
+        private static final long MASK = (1L << 48) - 1;
+
+        private long state;
+
+        ClumpRandom(long seed) {
+            super(seed);
+        }
+
+        @Override
+        public synchronized void setSeed(long seed) {
+            super.setSeed(seed);
+            state = (seed ^ MULTIPLIER) & MASK;
+        }
+
+        @Override
+        protected int next(int bits) {
+            state = (state * MULTIPLIER + ADDEND) & MASK;
+            return (int) (state >>> (48 - bits));
+        }
+    }
+
     private record PreparedDeposit(IrisDepositGenerator generator, boolean ore, List<PreparedClump> clumps) {
     }
 

core/src/test/java/art/arcane/iris/generation/stage/IrisDepositModifierProbabilityTest.java

@@ -19,6 +19,30 @@ public class IrisDepositModifierProbabilityTest {
         assertEquals(0.04D, accepted / (double) samples, 0.003D);
     }
 
+    @Test
+    public void clumpRandomMatchesRngDrawForDraw() {
+        RNG seeds = new RNG(-90181L);
+        for (int trial = 0; trial < 2_000; trial++) {
+            long seed = trial < 4 ? new long[]{0L, -1L, Long.MIN_VALUE, Long.MAX_VALUE}[trial] : seeds.nextLong();
+            RNG expected = new RNG(seed);
+            RNG actual = new IrisDepositModifier.ClumpRandom(seed);
+            for (int draw = 0; draw < 48; draw++) {
+                String label = "seed " + seed + " draw " + draw;
+                switch (draw % 8) {
+                    case 0 -> assertEquals(label, Float.floatToIntBits(expected.nextFloat()), Float.floatToIntBits(actual.nextFloat()));
+                    case 1 -> assertEquals(label, expected.nextInt(3), actual.nextInt(3));
+                    case 2 -> assertEquals(label, Double.doubleToLongBits(expected.nextDouble()), Double.doubleToLongBits(actual.nextDouble()));
+                    case 3 -> assertEquals(label, Double.doubleToLongBits(expected.d()), Double.doubleToLongBits(actual.d()));
+                    case 4 -> assertEquals(label, expected.i(-5, 17), actual.i(-5, 17));
+                    case 5 -> assertEquals(label, expected.nextInt(1_000_000_007), actual.nextInt(1_000_000_007));
+                    case 6 -> assertEquals(label, expected.nextLong(), actual.nextLong());
+                    default -> assertEquals(label, expected.nextBoolean(), actual.nextBoolean());
+                }
+            }
+            assertEquals(expected.getSeed(), actual.getSeed());
+        }
+    }
+
     @Test
     public void neighboringClumpChancesRemainIndependentAcrossBatchBoundaries() {
         int samples = 100_000;