Improved Dungeon Loot and Selection

DDLoot: Implemented a custom version of MC's generateChestContents() for
our own chests. It avoids two notable bugs that affect MC's version.

FillContainersOperation: Changed code to use
DDLoot.generateChestContents()

SchematicLoader: Fixed a bug in the way we calculated a seed for
selecting our dungeons that would cause certain seeds to dominate all
the others. Under certain circumstances, the function would only return
-1. That would make our dungeon selection severely biased. That was
resolved and the code was specifically tuned for seeding Java's Random
even for doors with nearly identical positions. The result was an
apparent major improvement in the randomness of dungeons.

ruins\rules.txt: Changed the dungeon generation rules to precisely match
the complicated scheme we had before. We're still using simple rules to
choose dungeons - I used a program to derive the effective distribution
of dungeon types that the old code would produce and converted it into
the current rule system.

StevenDimDoors/mod_pocketDim/SchematicLoader.java

@@ -42,7 +42,7 @@ public class SchematicLoader
 				if (dimList.get(destDimID).dungeonGenerator == null)
 				{
 					//TODO: We should centralize RNG initialization and world-seed modifiers for each specific application.
-					final long localSeed = world.getSeed() ^ 0x2F50DB9B4A8057E4L ^ computeDestinationHash(link);
+					final long localSeed = world.getSeed() ^ 0x2F50DB9B4A8057E4L ^ calculateDestinationSeed(link);
 					final Random random = new Random(localSeed);
 					
 					dungeonHelper.generateDungeonLink(link, dungeonHelper.getDimDungeonPack(originDimID), random);
@@ -155,43 +155,50 @@ public class SchematicLoader
 		return dungeon;
 	}
 	
-	private static long computeDestinationHash(LinkData link)
+	private static long calculateDestinationSeed(LinkData link)
 	{
 		//Time for some witchcraft.
 		//The code here is inspired by a discussion on Stack Overflow regarding hash codes for 3D.
 		//Source: http://stackoverflow.com/questions/9858376/hashcode-for-3d-integer-coordinates-with-high-spatial-coherence
 		
-		//Use 8 bits from Y and 24 bits from X and Z. Mix in 8 bits from the destination dim ID too - that means
+		//Use 8 bits from Y and 16 bits from X and Z. Mix in 8 bits from the destination dim ID too - that means
 		//even if you aligned two doors perfectly between two pockets, it's unlikely they would lead to the same dungeon.
+		//We map bits in reverse order to produce more varied RNG output for nearly-identical points. The reason is
+		//that Java's Random outputs the 32 MSBs of its internal state to produce its output. If the differences
+		//between two seeds are small (i.e. in the LSBs), then they will tend to produce similar random outputs anyway!
+		
+		//Only bother to assign the 48 least-significant bits since Random only takes those bits from its seed.
+		//NOTE: The casts to long are necessary to get the right results from the bit shifts!!!
 		
 		int bit;
 		int index;
 		long hash;
-		int w = link.destDimID;
-		int x = link.destXCoord;
-		int y = link.destYCoord;
-		int z = link.destZCoord;
+		final int w = link.destDimID;
+		final int x = link.destXCoord;
+		final int y = link.destYCoord;
+		final int z = link.destZCoord;
 		
 		hash = 0;
-		index = 0;
+		index = 48;
 		for (bit = 0; bit < 8; bit++)
 		{
-			hash |= ((w >> bit) & 1) << index;
-			index++;
-			hash |= ((x >> bit) & 1) << index;
-			index++;
-			hash |= ((y >> bit) & 1) << index;
-			index++;
-			hash |= ((z >> bit) & 1) << index;
-			index++;
+			hash |= (long) ((w >> bit) & 1) << index;
+			index--;
+			hash |= (long) ((x >> bit) & 1) << index;
+			index--;
+			hash |= (long) ((y >> bit) & 1) << index;
+			index--;
+			hash |= (long) ((z >> bit) & 1) << index;
+			index--;
 		}
-		for (; bit < 24; bit++)
+		for (; bit < 16; bit++)
 		{
-			hash |= ((x >> bit) & 1) << index;
-			index++;
-			hash |= ((z >> bit) & 1) << index;
-			index++;
+			hash |= (long) ((x >> bit) & 1) << index;
+			index--;
+			hash |= (long) ((z >> bit) & 1) << index;
+			index--;
 		}
+		
 		return hash;
 	}
 }